<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><div class="">Hello Swift development community,</div><div class=""><br class=""></div><div class="">Swift does a great job of protecting against undefined behavior--as long as you avoid "unsafe" APIs, that is. However, unsafe APIs are important for giving developers control over implementation details and performance. Naturally, the contract between unsafe APIs and the optimizer is crucial. When a developer uses an unsafe API, the rules governing safe, well-defined behavior must be clear. On the opposite end, the optimizer must know which assumptions it can make based on those rules. Simply saying that anything goes because "unsafe" is in the name is not helpful to this effort.</div><div class=""><br class=""></div><div class="">For a long time, I've wanted these rules nailed down. We have more users taking advantage of advanced features, and more optimizations that take advantage of assumptions guided by the type system. This seems like a particularly good time to resolve UnsafePointer semantics, considering the type system and UnsafePointer work that's been going on recently. Strict aliasing is something I would like addressed. If we do nothing here, then we will end up by default inheriting C/C++ semantics, as with any language that relies on a C/C++ backend. In other words, developers will be forced to write code with technically undefined behavior and rely on the compiler to be smart enough to recognize and recover from common patterns. Or we can take advantage of this opportunity and instead adopt a sound memory model with respect to aliasing.</div><div class=""><br class=""></div><div class="">This proposal is only an RFC at this point. I'm sending it out now to allow for plenty of time for discussion (or advance warning). Keep in mind that it could change considerably before it goes up for review.</div></div><div class=""><br class=""></div><div class="">-Andy</div><div class=""><br class=""></div><div class=""><h1 class="" style="box-sizing: border-box; font-size: 2.25em; margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.2; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;">UnsafeBytePointer API for In-Memory Layout</h1><ul class="" style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><li class="" style="box-sizing: border-box;">Proposal: <a href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md" class="" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;">SE-NNNN</a></li><li class="" style="box-sizing: border-box;">Author(s): <a href="https://github.com/atrick" class="" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;">Andrew Trick</a></li><li class="" style="box-sizing: border-box;">Status: <span class="" style="box-sizing: border-box;"><a href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#rationale" class="" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;">Awaiting review</a></span></li><li class="" style="box-sizing: border-box;">Review manager: TBD</li></ul><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-introduction" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#introduction" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Introduction</h2><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> and <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeMutable</code> refer to a typed region of memory, and the compiler must be able to assume that <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> element (<code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Pointee</code>) type is consistent with other access to the same memory. See <a href="https://github.com/atrick/swift/blob/type-safe-mem-docs/docs/TypeSafeMemory.rst" class="" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;">proposed Type Safe Memory Access documentation</a>. Consequently, inferred conversion between <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> element types exposes an easy way to abuse the type system. No alternative currently exists for manual memory layout and direct access to untyped memory, and that leads to an overuse of <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code>. These uses of <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code>, which depend on pointer type conversion, make accidental type punning likely. Type punning via <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> is semantically undefined behavior and de facto undefined behavior given the optimizer's long-time treatment of <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code>.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">In this document, all mentions of <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> also apply to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeMutablePointer</code>.</p><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-motivation" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#motivation" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Motivation</h2><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">To avoid accidental type punning, we should prohibit inferred conversion between <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<T></code> and <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<U></code> unless the target of the conversion is an untyped or nondereferenceable pointer (currently represented as <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Void></code>).</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">To support this change we should introduce a new pointer type that does not bind the type of its <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Pointee</code>. Such a new pointer type would provide an ideal foundation for an API that allows byte-wise pointer arithmetic and a legal, well-defined means to access an untyped region of memory.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">As motivation for such an API, consider that an <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Void></code> or <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">OpaquePointer</code> may be currently be obtained from an external API. However, the developer may know the memory layout and may want to read or write elements whose types are compatible with that layout. This a reasonable use case, but unless the developer can guarantee that all accesses to the same memory location have the same type, then they cannot use <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> to access the memory without risking undefined behavior.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">An <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> example, using a new proposed API is included below.</p><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-proposed-solution" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#proposed-solution" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Proposed solution</h2><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Introduce an <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> type along with an API for obtaining a <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> value at a relative byte offset and loading and storing arbitrary types at that location.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Statically prohibit inferred <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> conversion while allowing inferred <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code>conversion.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> meets multiple requirements:</p><ol class="" style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><li class="" style="box-sizing: border-box;">An untyped pointer to memory</li><li class="" style="box-sizing: border-box;">Pointer arithmetic within byte-addressable memory</li><li class="" style="box-sizing: border-box;">Type-unsafe access to memory (legal type punning)</li></ol><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> will replace <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeMutablePointer<Void></code> as the representation for untyped memory. For API clarify we could consider a typealias for <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">VoidPointer</code>. I don't think a separate <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">VoidPointer</code> type would be useful--there's no danger that <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> will be casually dereferenced, and don't see the danger in allowing pointer arithmetic since the only reasonable interpretation is that of a byte-addressable memory.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Providing an API for type-unsafe memory access would not serve a purpose without the ability to compute byte offsets. Of course, we could require users to convert back and forth using bitPatterns, but I think that would be awkward and only obscure the purpose of the <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> type.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">In this proposal, UnsafeBytePointer does not specify mutability. Adding an UnsafeMutableBytePointer would be straightforward, but adding another pointer type needs strong justification. I expect to get input from the community on this. If we agree that the imported type for <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">const void*</code> should be UnsafeBytePointer, then we probably need UnsafeMutablePointer to handle interoperability.</p><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-detailed-design" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#detailed-design" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Detailed design</h2><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">The public API is shown here. For details and comments, see the <a href="https://github.com/atrick/swift/commits/unsafeptr_convert" class="" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;">unsafeptr_convert branch</a>.</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">struct</span> UnsafeBytePointer <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Hashable</span>, _Pointer {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> _rawValue: Builtin<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>RawPointer
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> hashValue: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> {<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">...</span>}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(_ <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(_ <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafeMutablePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>?<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(_ <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>?)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>?<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(_ <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafeMutablePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>?)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(_ <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> OpaquePointer<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>?<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(_ <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> OpaquePointer<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>?)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>?(bitPattern: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>?(bitPattern: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">load</span><T>(_ <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">Type</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> T
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">@warn_unused_result</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(allocatingBytes size: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>, alignedTo: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">@warn_unused_result</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(allocatingCapacity count: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>, of: T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">Type</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">deallocateBytes</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box;">size</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>, alignedTo: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">deallocateCapacity</span><T>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box;">num</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>, of: T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">Type</span>)
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// Returns a pointer one byte after the initialized memory.</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">initialize</span><T>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">with</span> <span class="pl-smi" style="box-sizing: border-box;">newValue</span>: T, count: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// Returns a pointer one byte after the initialized memory.</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">initialize</span><T>(from: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>, count: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">initializeBackward</span><T>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">from</span> <span class="pl-smi" style="box-sizing: border-box;">source</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>, count: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">deinitialize</span><T>(_ <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> T<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">Type</span>, count: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> OpaquePointer {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(_ <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> UnsafeBytePointer)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(bitPattern: UnsafeBytePointer)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(bitPattern: UnsafeBytePointer)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> UnsafeBytePointer <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> RandomAccessIndex {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">typealias</span> Distance <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">successor</span>() <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">predecessor</span>() <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">distance</span>(to <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> UnsafeBytePointer) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">advanced</span>(by <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">==</span> (lhs: UnsafeBytePointer, rhs: UnsafeBytePointer) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Bool</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);"><</span> (lhs: UnsafeBytePointer, rhs: UnsafeBytePointer) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Bool</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">+</span> (lhs: UnsafeBytePointer, rhs: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">+</span> (lhs: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>, rhs: UnsafeBytePointer) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">-</span> (lhs: UnsafeBytePointer, rhs: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">-</span> (lhs: UnsafeBytePointer, rhs: UnsafeBytePointer) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">+=</span> (lhs: <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">inout</span> <span class="pl-smi" style="box-sizing: border-box;">UnsafeBytePointer</span>, rhs: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">-=</span> (lhs: <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">inout</span> <span class="pl-smi" style="box-sizing: border-box;">UnsafeBytePointer</span>, rhs: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>)
</pre></div><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Occasionally, we need to convert from a <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> to an <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code>. This should only be done in very rare circumstances when the author understands the compiler's strict type rules for <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code>. Although this could be done by casting through an <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">OpaquePointer</code>, an explicit, designated unsafe pointer cast API would makes the risks more obvious and self-documenting. For example:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafePointer</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(_ from: UnsafeBytePointer, toPointee: Pointee<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>type)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafeMutablePointer</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(_ from: UnsafeBytePointer, toPointee: Pointee<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>type)
}</pre></div><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Similarly, conversion between <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> types must now be spelled with an explicitly <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Pointee</code> type:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafePointer</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>U<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(_ from: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>U<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>, toPointee: Pointee<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">Type</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>U<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(_ from: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafeMutablePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>U<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>, toPointee: Pointee<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">Type</span>)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">extension</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafeMutablePointer</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>U<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(_ from: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafeMutablePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span>U<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>, toPointee: Pointee<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">Type</span>)
}</pre></div><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-impact-on-existing-code" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#impact-on-existing-code" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Impact on existing code</h2><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">The largest impact of this change is that <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">void*</code> and <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">const void*</code> are imported as UnsafeBytePointer. This impacts many public APIs, but with implicit argument conversion should not affect typical uses of those APIs.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Any Swift projects that rely on type inference to convert between <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> types will need to take action. The developer needs to determine whether type punning is necessary. If so, they must migrate to the <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> API. Otherwise, they can work around the new restriction by using a <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">toPointee</code>, or <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">mutating</code> label.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Disallowing inferred <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> direct conversion requires some standard library code to use an explicit <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">toPointee</code>label for unsafe conversions that may violate strict aliasing.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">All occurrences of <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Unsafe[Mutable]Pointer<Void></code> in the standard library are converted to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code>. e.g. <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">unsafeAddress()</code> now returns <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code>, not <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Void></code>.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Some occurrences of <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Unsafe[Mutable]Pointer<Pointee></code> in the standard library are replaced with <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code>, either because the code was playing too loosely with strict aliasing rules, or because the code actually wanted to perform pointer arithmetic on byte-addresses.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">StringCore.baseAddress</code> changes from <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">OpaquePointer</code> to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> because it is computing byte offsets and accessing the memory. <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">OpaquePointer</code> is meant for bridging, but should be truly opaque; that is, nondereferenceable and not involved in address computation.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">The <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">StringCore</code> implementation does a considerable amount of casting between different views of the <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">String</code> storage. The current implementation already demonstrates some awareness of strict aliasing rules. The rules are generally followed by ensuring that the <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">StringBuffer</code> only be accessed using the appropriate <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">CodeUnit</code> within Swift code. For interoperability and optimization, String buffers frequently need to be cast to and from <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">CChar</code>. This is valid as long access to the buffer from Swift is guarded by dynamic checks of the encoding type. These unsafe, but dynamically legal conversion points will now be labeled with <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">toPointee</code>.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">CoreAudio</code> utilities now use an UnsafeBytePointer.</p><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-implementation-status" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#implementation-status" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Implementation status</h2><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">On my <a href="https://github.com/atrick/swift/commits/unsafeptr_convert" class="" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;">unsafeptr_convert branch</a>, I've made most of the necessary changes to support the addition of <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code>and the removal of inferred <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> conversion.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">There are a several things going on here in order to make it possible to build the standard library with the changes:</p><ul class="" style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">A new <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> type is defined.</p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">The type system imports <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">void*</code> as UnsafeBytePointer.</p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">The type system handles implicit conversions to UnsafeBytePointer.</p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;"><code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> replaces both <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Void></code> and <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeMutablePointer<Void></code>.</p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">The standard library was relying on inferred UnsafePointer conversion in over 100 places. Most of these conversions now either take an explicit label, such as 'toPointee', 'mutating'. Some have been rewritten.</p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">Several places in the standard library that were playing loosely with strict aliasing or doing bytewise pointer arithmetic now use UnsafeBytePointer instead.</p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">Explicit labeled <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Unsafe[Mutable]Pointer</code> initializers are added.</p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">The inferred <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Unsafe[Mutable]Pointer</code> conversion is removed.</p></li></ul><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">TODO:</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Once this proposal is accepted, and the rules for casting between pointers types have been decided, we need to finish implementing the type system support. The current implementation (intentionally) breaks a few tests in pointer_conversion.swift. We also need to ensure that interoperability requirements are met. Currently, many argument casts to be explicitly labeled. The current implementation also makes it easy for users to hit an "ambiguous use of 'init'" error when relying on implicit argument conversion.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Additionally:</p><ul class="" style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">A name mangled abbreviation needs to be created for UnsafeBytePointer.</p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">The StringAPI tests should probably be rewritten with <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code>.</p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">The NSStringAPI utilities and tests may need to be ported to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code></p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;">The CoreAudio utilities and tests may need to be ported to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code>.</p></li></ul><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-alternatives-considered" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#alternatives-considered" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Alternatives considered</h2><h3 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.43; font-size: 1.5em; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-existing-workaround" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#existing-workaround" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1.2;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Existing workaround</h3><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">In some cases, developers can safely reinterpret values to achieve the same effect as type punning:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> ptrI32 <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UnsafeMutablePointer</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);"><</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int32</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">></span>(allocatingCapacity: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>)
ptrI32[<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span>] <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int32</span>()
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> u <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">unsafeBitCast</span>(ptrI32[<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span>], to: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">self</span>)</pre></div><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Note that all access to the underlying memory is performed with the same element type. This is perfectly legitimate, but simply isn't a complete solution. It also does not eliminate the inherent danger in declaring a typed pointer and expecting it to point to values of a different type.</p><h3 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.43; font-size: 1.5em; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-discarded-alternatives" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#discarded-alternatives" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1.2;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Discarded alternatives</h3><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">We considered adding a <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">typePunnedMemory</code> property to the existing <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Unsafe[Mutabale]Pointer</code> API. This would provide a legal way to access a potentially type punned <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">Unsafe[Mutabale]Pointer</code>. However, it would certainly cause confusion without doing much to reduce likelihood of programmer error. Furthermore, there are no good use cases for such a property evident in the standard library.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">The opaque <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">_RawByte</code> struct is a technique that allows for byte-addressable buffers while hiding the dangerous side effects of type punning (a _RawByte could be loaded but it's value cannot be directly inspected). <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<_RawByte></code> is a clever alternative to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code>. However, it doesn't do enough to prevent undefined behavior. The loaded <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">_RawByte</code> would naturally be accessed via <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">unsafeBitCast</code>, which would mislead the author into thinking that they have legally bypassed the type system. In actuality, this API blatantly violates strict aliasing. It theoretically results in undefined behavior as it stands, and may actually exhibit undefined behavior if the user recovers the loaded value.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">To solve the safety problem with <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<_RawByte></code>, the compiler could associate special semantics with a <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code> bound to this concrete generic parameter type. Statically enforcing casting rules would be difficult if not impossible without new language features. It would also be impossible to distinguish between typed and untyped pointer APIs. For example, <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<T>.load<U></code> would be a nonsensical vestige.</p><h3 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.43; font-size: 1.5em; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-alternate-proposal-for-void-type" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#alternate-proposal-for-void-type" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1.2;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Alternate proposal for <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: inherit; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">void*</code> type</h3><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Changing the imported type for <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">void*</code> will be somewhat disruptive. Furthermore, this proposal currently drops the distinction between <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">void*</code> and <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">const void*</code>--an obvious loss of API information.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">We could continue to import <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">void*</code> as <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeMutablePointer<Void></code> and <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">const void*</code> as <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Void></code>, which will continue to serve as an "opaque" untyped pointer. Converting to UnsafeBytePointer would be necesarry to perform pointer arithmetic or to conservatively handle possible type punning.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">This alternative is <em class="" style="box-sizing: border-box;">much</em> less disruptive, but we are left with two forms of untyped pointer, one of which (<code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer</code>) the type system somewhat conflates with typed pointers.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">Given the current restrictions of the language, it's not clear how to statically enforce the necessary rules for casting<code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Void></code> once general <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<T></code> conversions are disallowed. The following conversions should be inferred, and implied for function arguments (ignoring mutability):</p><ul class="" style="box-sizing: border-box; padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;"><code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<T></code> to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Void></code></p></li><li class="" style="box-sizing: border-box;"><p class="" style="box-sizing: border-box; margin-top: 16px; margin-bottom: 16px;"><code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Void></code> to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code></p></li></ul><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">I did not implement this simpler design because my primary goal was to enforce legal pointer conversion and rid Swift code of undefined behavior. I can't do that while allowing UnsafePointer conversions.</p><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-api-improvements" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#api-improvements" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>API improvements</h2><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">As proposed, the <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">initialize</code> API infers the stored value:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">initialize</span><T>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">with</span> <span class="pl-smi" style="box-sizing: border-box;">newValue</span>: T, count: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer</pre></div><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">This is somewhat dangerous because the developer may not realize the size of the object(s) that will be written to memory. This can be easily asserted by checking the return pointer:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> newptr <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> ptr<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">initialize</span>(with: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">3</span>)
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">assert</span>(newptr <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-</span> ptr <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">8</span>)</pre></div><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">As an alternative, we could force the user to provide the expected type name in the <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">initialize</code> invocation:</p><div class="highlight highlight-source-swift" style="box-sizing: border-box; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;"><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">initialize</span><T>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box;">T</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">Type</span>, <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">with</span> <span class="pl-smi" style="box-sizing: border-box;">newValue</span>: T, count: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer</pre></div><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-future-improvements" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#future-improvements" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>Future improvements</h2><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);"><code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code> should eventually support unaligned memory access. I believe that we will eventually have a modifier that allows "packed" struct members. At that time we may also want to add a "packed" flag to <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeBytePointer</code>'s <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">load</code> and <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">initialize</code> methods.</p><p class="" style="box-sizing: border-box; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);">When accessing a memory buffer, it is generally convenient to cast to a type with known layout and compute offsets relative to the type's size. This is how <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Pointee></code> works. A generic <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafeTypePunnedPointer<Pointee></code> could be introduced with the same interface as <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">UnsafePointer<Pointer></code>, but without the strict aliasing requirements. This seems like an overdesign simply to avoid calling <code class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; padding: 0.2em 0px; margin: 0px; background-color: rgba(0, 0, 0, 0.0392157); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px;">sizeof()</code> in an rare use case, but nothing prevents adding this type later.</p><h2 class="" style="box-sizing: border-box; margin-top: 1em; margin-bottom: 16px; line-height: 1.225; font-size: 1.75em; padding-bottom: 0.3em; border-bottom-width: 1px; border-bottom-style: solid; border-bottom-color: rgb(238, 238, 238); color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);"><a id="user-content-unsafebytepointer-example" class="anchor" href="https://github.com/atrick/swift-evolution/blob/voidpointer/proposals/XXXX-unsafebytepointer.md#unsafebytepointer-example" aria-hidden="true" style="box-sizing: border-box; background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; display: inline-block; padding-right: 2px; margin-left: -18px; line-height: 1;"><svg aria-hidden="true" class="octicon octicon-link" height="16" version="1.1" viewBox="0 0 16 16" width="16"><path d="M4 9h1v1h-1c-1.5 0-3-1.69-3-3.5s1.55-3.5 3-3.5h4c1.45 0 3 1.69 3 3.5 0 1.41-0.91 2.72-2 3.25v-1.16c0.58-0.45 1-1.27 1-2.09 0-1.28-1.02-2.5-2-2.5H4c-0.98 0-2 1.22-2 2.5s1 2.5 2 2.5z m9-3h-1v1h1c1 0 2 1.22 2 2.5s-1.02 2.5-2 2.5H9c-0.98 0-2-1.22-2-2.5 0-0.83 0.42-1.64 1-2.09v-1.16c-1.09 0.53-2 1.84-2 3.25 0 1.81 1.55 3.5 3 3.5h4c1.45 0 3-1.69 3-3.5s-1.5-3.5-3-3.5z"></path></svg></a>UnsafeBytePointer example</h2><div class="highlight highlight-source-swift" style="box-sizing: border-box; color: rgb(51, 51, 51); font-family: 'Helvetica Neue', Helvetica, 'Segoe UI', Arial, freesans, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255); margin-bottom: 0px !important;"><pre class="" style="box-sizing: border-box; font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 14px; margin-top: 0px; margin-bottom: 0px; line-height: 1.45; padding: 16px; overflow: auto; background-color: rgb(247, 247, 247); border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-wrap: normal; word-break: normal;"><span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">/// An example of using UnsafeBytePointer to implement manual memory layout.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">/// A Buffer for reading and writing basic types at a fixed address.</span>
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">/// Indirection allows the buffer to refer to mutable state elsewhere.</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">struct</span> MessageBuffer {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> ptr: UnsafeBytePointer
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">enum</span> IndirectFlag { <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> Direct, Indirect }
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">private</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">getPointer</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">atOffset</span> <span class="pl-smi" style="box-sizing: border-box;">n</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>, <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box;">isIndirect</span>: IndirectFlag)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> UnsafeBytePointer {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">switch</span> isIndirect {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Indirect:
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> (ptr <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">+</span> n)<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>load(UnsafeBytePointer<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">self</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Direct:
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> ptr <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">+</span> n
}
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">readUInt32</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">atOffset</span> <span class="pl-smi" style="box-sizing: border-box;">n</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>, <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box;">isIndirect</span>: IndirectFlag) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> getPointer(atOffset: n, isIndirect)<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>load(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">self</span>)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">readFloat32</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">atOffset</span> <span class="pl-smi" style="box-sizing: border-box;">n</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>, <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box;">isIndirect</span>: IndirectFlag) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Float32</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> getPointer(atOffset: n, isIndirect)<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>load(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Float32</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">self</span>)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">writeUInt32</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box;">val</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span>, <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">atOffset</span> <span class="pl-smi" style="box-sizing: border-box;">n</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>) {
getPointer(atOffset: n, <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Direct)<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">initialize</span>(with: val)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">writeFloat32</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box;">val</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Float32</span>, <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">atOffset</span> <span class="pl-smi" style="box-sizing: border-box;">n</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>) {
getPointer(atOffset: n, <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Direct)<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">initialize</span>(with: val)
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">writeIndirect</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">_</span> <span class="pl-smi" style="box-sizing: border-box;">ptr</span>: UnsafeBytePointer, <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">atOffset</span> <span class="pl-smi" style="box-sizing: border-box;">n</span>: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span>) {
getPointer(atOffset: n, <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Direct)<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">initialize</span>(with: ptr)
}
}
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">/// Encoded message format.</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">struct</span> MessageFormat <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> Sequence, IteratorProtocol {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">typealias</span> Element <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> MessageFormat
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">private</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">static</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> maxFormatFields <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">32</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">/</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">4</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">static</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> maxBufferBytes <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> maxFormatFields <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">*</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">sizeof</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt</span>)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> formatCode: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> elementCode: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> offset: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">init</span>(bitPattern: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span>) {
formatCode <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> bitPattern
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">enum</span> Kind {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> None, Reserved, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span>, <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Float32</span>, IndirectUInt32, IndirectFloat32
}
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">/// The first field's kind.</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> kind <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> Kind {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">get</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">switch</span> elementCode {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> 0x0: <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> Kind<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>None
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> 0x2: <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> Kind<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> 0x3: <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> Kind<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Float32</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> 0x6: <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> Kind<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>IndirectUInt32
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> 0x7: <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> Kind<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>IndirectFloat32
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">default</span>: <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> Kind<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Reserved
}
}
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">elementSize</span>() <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Int</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> (elementCode <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">&</span> 0x4) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">?</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">sizeof</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt</span>) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">:</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">4</span>
}
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">/// Get the format for the next element.</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">mutating</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">next</span>() <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> Element? {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">if</span> elementCode <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">!=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span> {
offset <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">+=</span> elementSize()
}
elementCode <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> formatCode <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">&</span> 0xF
formatCode <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">>>=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">4</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">if</span> kind <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">==</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>None {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">nil</span>
}
<span class="pl-c" style="box-sizing: border-box; color: rgb(150, 152, 150);">// align to the next element size</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> offsetMask <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> elementSize() <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">1</span>
offset <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> (offset <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">+</span> offsetMask) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">&</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">~</span>offsetMask
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">self</span>
}
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">createBuffer</span>() <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> MessageBuffer {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> MessageBuffer(ptr: UnsafeBytePointer(
allocatingBytes: MessageFormat<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>maxBufferBytes, alignedTo: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">sizeof</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt</span>)))
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">destroy</span>(buffer: MessageBuffer) {
buffer<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>ptr<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>deallocateBytes(MessageFormat<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>maxBufferBytes,
alignedTo: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">sizeof</span>(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt</span>))
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> sharedInt: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">42</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">var</span> sharedFloat: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Float32</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">16</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">25</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">generateMessage</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">inBuffer</span> <span class="pl-smi" style="box-sizing: border-box;">mb</span>: MessageBuffer) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> MessageFormat {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> mf <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> MessageFormat(bitPattern: 0x06727632)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">for</span> field <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> mf {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">switch</span> field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>kind {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span>:
mb<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>writeUInt32(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">66</span>, atOffset: field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>offset)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Float32</span>:
mb<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>writeFloat32(<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">41</span><span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">625</span>, atOffset: field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>offset)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>IndirectUInt32:
mb<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>writeIndirect(<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">&</span>sharedInt, atOffset: field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>offset)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>IndirectFloat32:
mb<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>writeIndirect(<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">&</span>sharedFloat, atOffset: field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>offset)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>None:
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">fallthrough</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Reserved:
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> MessageFormat(bitPattern: <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">0</span>)
}
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> mf
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">handleMessage</span>(<span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">buffer</span> <span class="pl-smi" style="box-sizing: border-box;">mb</span>: MessageBuffer, format: MessageFormat) <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">-></span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Bool</span> {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">for</span> field <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">in</span> format {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">switch</span> field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>kind {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">UInt32</span>:
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">print</span>(mb<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>readUInt32(atOffset: field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>offset, <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Direct))
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span><span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">Float32</span>:
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">print</span>(mb<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>readFloat32(atOffset: field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>offset, <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Direct))
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>IndirectUInt32:
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">print</span>(mb<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>readUInt32(atOffset: field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>offset, <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Indirect))
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>IndirectFloat32:
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">print</span>(mb<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>readFloat32(atOffset: field<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>offset, <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Indirect))
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>None:
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">fallthrough</span>
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">case</span> <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">.</span>Reserved:
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">false</span>
}
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">return</span> <span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">true</span>
}
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">func</span> <span class="pl-en" style="box-sizing: border-box; color: rgb(121, 93, 163);">runProgram</span>() {
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> mb <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> createBuffer()
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">let</span> mf <span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">=</span> generateMessage(inBuffer: mb)
<span class="pl-k" style="box-sizing: border-box; color: rgb(167, 29, 93);">if</span> handleMessage(buffer: mb, format: mf) {
<span class="pl-c1" style="box-sizing: border-box; color: rgb(0, 134, 179);">print</span>(<span class="pl-s" style="box-sizing: border-box; color: rgb(24, 54, 145);"><span class="pl-pds" style="box-sizing: border-box;">"</span>Done<span class="pl-pds" style="box-sizing: border-box;">"</span></span>)
}
destroy(buffer: mb)
}
runProgram()</pre></div></div><div class=""><br class=""></div></body></html>