<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Sep 28, 2016, at 4:47 PM, Kevin Ballard <<a href="mailto:kevin@sb.org" class="">kevin@sb.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">On Wed, Sep 28, 2016, at 02:27 PM, plx via swift-evolution wrote:<br class=""></div><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class="">+1 to have something *like* this, but a few questions.<br class=""></div><div class=""><br class=""></div><div class="">Is there a specific reason `IndexedSequence` isn’t `IndexedCollection`, conforming to `Collection` (and once conditional conformances are available picking up `BidirectionalCollection` and `RandomAccessCollection` when possible?).<br class=""></div></blockquote><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">This is already being discussed in this thread, but the simple answer is that adds complexity and it's not obvious that it's worth the additional complexity.</div></div></blockquote><div><br class=""></div><div>As it can be done as trivial, "pass-through" boilerplate:</div><div><br class=""></div><div> struct IndexedCollection<C:Collection> :Collection {</div><div> typealias Index = C.Index</div><div> typealias Indices = C.Indices</div><div><br class=""></div><div> let base: C</div><div> </div><div> subscript(i: Index) -> (Index,C.Iterator.Element) { return (i,base[i]) }</div><div> </div><div>}</div><div><br class=""></div><div>…(and so on and so forth) it’s about as trivial to implement as any `Collection` is going to be…which is why I was a bit surprised it wasn’t part of the proposal.</div><div><br class=""></div><div>If you’re worried about performance vis-a-vis lazy collections you could also store the `base.indices` and use it instead of `base` but even that should leave the implementation almost entirely boilerplate-ish.</div><div><br class=""></div><div>Sure it’s a bit annoying to write it all out but I’m not seeing a lot of complexity really; I might be missing something?</div><div><br class=""></div><blockquote type="cite" class=""><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class="">Secondly, can you provide more detail on the proposed implementation? <br class=""></div><div class=""><br class=""></div><div class="">Are you just walking the index forward and subscripting the base in the iterator, or something fancier?<br class=""></div></blockquote><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Yeah, that's what it would be. Something like<br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">sequence(state: base.indices, next: {<br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""> guard let idx = $0.next() else { return nil }<br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""> return (idx, base[idx])<br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">})<br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">except done as a concrete type.</div></div></blockquote><div><br class=""></div><div>I assume the above is closer to this?</div><div><br class=""></div><blockquote type="cite" class=""><div class="">sequence(state: base.indices.makeIterator(), next: {<br class=""></div><div class=""> guard let idx = $0.next() else { return nil }<br class=""></div><div class=""> return (idx, base[idx])<br class=""></div><div class="">})<br class=""></div></blockquote><div><br class=""></div><div>The way the proposal was worried I was concerned the “only calculate each index once” bit would be a bit expensive when not really necessary, but deferring to the implementation of `indices` seems perfectly reasonable to me.</div><div class=""><div class=""><br class=""></div></div><blockquote type="cite" class=""><div class=""><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">-Kevin</div><div style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><div class=""><blockquote type="cite" class=""><div class="">On Sep 28, 2016, at 12:55 PM, Erica Sadun via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""></div><div class=""><br class=""></div><div class=""><div style="word-wrap: break-word; -webkit-line-break: after-white-space;" class=""><div class="">Gist here: <a href="https://gist.github.com/erica/2b2d92e6db787d001c689d3e37a7c3f2" class="">https://gist.github.com/erica/2b2d92e6db787d001c689d3e37a7c3f2</a><br class=""></div><div class=""><br class=""></div><div class=""><h1 style="margin-right: 0px; margin-bottom: 16px; margin-left: 0px; line-height: 1.25; 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: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255); margin-top: 0px !important;" class="">Introducing <code style="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;" class="">indexed()</code> collections<br class=""></h1><ul style="padding-left: 2em; margin-top: 0px; margin-bottom: 16px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255);" class=""><li class="">Proposal: TBD<br class=""></li><li style="margin-top: 0.25em;" class="">Author: <a href="https://github.com/erica" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;" class="">Erica Sadun</a>, <a href="https://github.com/natecook1000" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;" class="">Nate Cook</a>, <a href="https://github.com/jtbandes" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;" class="">Jacob Bandes-Storch</a>, <a href="https://github.com/kballard" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;" class="">Kevin Ballard</a><br class=""></li><li style="margin-top: 0.25em;" class="">Status: TBD<br class=""></li><li style="margin-top: 0.25em;" class="">Review manager: TBD<br class=""></li></ul><h2 style="margin-top: 24px; margin-bottom: 16px; line-height: 1.25; 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: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a href="https://gist.github.com/erica/2b2d92e6db787d001c689d3e37a7c3f2#introduction" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; float: left; padding-right: 4px; line-height: 1;" class=""></a>Introduction<br class=""></h2><p style="margin-top: 0px; margin-bottom: 16px;" class=""><span class="highlight" style="background-color: rgb(255, 255, 255);"><span class="colour" style="color: rgb(51, 51, 51);"><span class="font" style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol';"><span class="size" style="font-size: 16px;">This proposal introduces <code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;" class="">indexed()</code> to the standard library, a method on collections that returns an (index, element) tuple sequence.</span></span></span></span><br class=""></p><p style="margin-top: 0px; margin-bottom: 16px;" class=""><span class="highlight" style="background-color: rgb(255, 255, 255);"><span class="colour" style="color: rgb(51, 51, 51);"><span class="font" style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol';"><span class="size" style="font-size: 16px;">Swift-evolution thread: <a href="https://gist.github.com/erica/tbd" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none;" class="">TBD</a></span></span></span></span><br class=""></p><h2 style="margin-top: 24px; margin-bottom: 16px; line-height: 1.25; 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: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a href="https://gist.github.com/erica/2b2d92e6db787d001c689d3e37a7c3f2#motivation" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; float: left; padding-right: 4px; line-height: 1;" class=""></a>Motivation<br class=""></h2><p style="margin-top: 0px; margin-bottom: 16px;" class=""><span class="highlight" style="background-color: rgb(255, 255, 255);"><span class="colour" style="color: rgb(51, 51, 51);"><span class="font" style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol';"><span class="size" style="font-size: 16px;">The standard library's <code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;" class="">enumerated()</code> method returns a sequence of pairs enumerating a sequence. The pair's first member is a monotonically incrementing integer starting at zero, and the second member is the corresponding element of the sequence. When working with arrays, the integer is coincidentally the same type and value as an <code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;" class="">Array</code> index but the enumerated value is not generated with index-specific semantics. This may lead to confusion when developers attempt to subscript a non-array collection with enumerated integers. It can introduce serious bugs when developers use <code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;" class="">enumerated()</code>-based integer subscripting with non-zero-based array slices.</span></span></span></span><br class=""></p><p style="margin-top: 0px; margin-bottom: 16px;" class=""><span class="highlight" style="background-color: rgb(255, 255, 255);"><span class="colour" style="color: rgb(51, 51, 51);"><span class="font" style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol';"><span class="size" style="font-size: 16px;">Indices have a specific, fixed meaning in Swift, which are used to create valid collection subscripts. This proposal introduces <code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;" class="">indexed()</code> to produce a more semantically relevant sequence by pairing a collection's <code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;" class="">indices</code> with its members. While it is trivial to create a solution in Swift, the most common developer approach shown here calculates indexes twice: </span></span></span></span><br class=""></p><pre style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; margin-top: 0px; margin-bottom: 16px; line-height: 1.45; word-wrap: normal; 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; color: rgb(51, 51, 51);" class=""><code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; padding: 0px; margin: 0px; background-color: transparent; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; word-break: normal; border: 0px; display: inline; overflow: visible; line-height: inherit; word-wrap: normal;" class="">extension Collection {
/// Returns a sequence of pairs (*idx*, *x*), where *idx* represents a
/// consecutive collection index, and *x* represents an element of
/// the sequence.
func indexed() -> Zip2Sequence<Self.Indices, Self> {
return zip(indices, self)
}
}
</code><br class=""></pre><p style="margin-top: 0px; margin-bottom: 16px;" class=""><span class="highlight" style="background-color: rgb(255, 255, 255);"><span class="colour" style="color: rgb(51, 51, 51);"><span class="font" style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol';"><span class="size" style="font-size: 16px;">Incrementing an index in some collections can be unnecessarily costly. In a lazy filtered collection, an index increment is potentially O(N). We feel this is better addressed introducing a new function into the Standard Library to provide a more efficient design that avoids the attractive nuisance of the "obvious" solution.</span></span></span></span><br class=""></p><h2 style="margin-top: 24px; margin-bottom: 16px; line-height: 1.25; 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: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a href="https://gist.github.com/erica/2b2d92e6db787d001c689d3e37a7c3f2#detailed-design" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; float: left; padding-right: 4px; line-height: 1;" class=""></a>Detailed Design<br class=""></h2><p style="margin-top: 0px; margin-bottom: 16px;" class=""><span class="highlight" style="background-color: rgb(255, 255, 255);"><span class="colour" style="color: rgb(51, 51, 51);"><span class="font" style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol';"><span class="size" style="font-size: 16px;">Our vision of <code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;" class="">indexed()</code> bypasses duplicated index generation with their potentially high computation costs. We'd create an iterator that calculates each index once and then applies that index to subscript the collection. Implementation would take place through <code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;" class="">IndexedSequence</code>, similar to <code style="font-family: Consolas, 'Liberation Mono', Menlo, Courier, monospace; font-size: 13.600000381469727px; 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;" class="">EnumeratedSequence</code>.</span></span></span></span><br class=""></p><h2 style="margin-top: 24px; margin-bottom: 16px; line-height: 1.25; 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: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a href="https://gist.github.com/erica/2b2d92e6db787d001c689d3e37a7c3f2#impact-on-existing-code" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; float: left; padding-right: 4px; line-height: 1;" class=""></a>Impact on Existing Code<br class=""></h2><p style="margin-top: 0px; margin-bottom: 16px;" class=""><span class="highlight" style="background-color: rgb(255, 255, 255);"><span class="colour" style="color: rgb(51, 51, 51);"><span class="font" style="font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol';"><span class="size" style="font-size: 16px;">This proposal is purely additive and has no impact on existing code.</span></span></span></span><br class=""></p><h2 style="margin-top: 24px; margin-bottom: 16px; line-height: 1.25; 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: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; background-color: rgb(255, 255, 255);" class=""><a href="https://gist.github.com/erica/2b2d92e6db787d001c689d3e37a7c3f2#alternatives-considered" style="background-color: transparent; -webkit-text-decoration-skip: objects; color: rgb(64, 120, 192); text-decoration: none; float: left; padding-right: 4px; line-height: 1;" class=""></a>Alternatives Considered<br class=""></h2><div style="margin-top: 0px; color: rgb(51, 51, 51); font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol'; font-size: 16px; background-color: rgb(255, 255, 255); margin-bottom: 0px !important;" class="">Not yet<br class=""></div></div></div><div class="">_______________________________________________<br class=""></div><div class="">swift-evolution mailing list<br class=""></div><div class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""></div><div class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></div></blockquote></div><div class=""><br class=""></div><div class=""><u class="">_______________________________________________</u><br class=""></div><div class="">swift-evolution mailing list<br class=""></div><div class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""></div><div class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></div></blockquote></div></blockquote></div><br class=""></body></html>