<div dir="ltr"><div class="gmail_extra"><div class="gmail_quote">On Mon, Jul 18, 2016 at 4:09 PM, Robert Widmann via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word">Hello all,<div><br></div><div>TJ Usiyan, Harlan Haskins, and I have been working on a proposal to rework qualified imports and introduce an explicit module system to Swift that we’d like to publish for your viewing pleasure.</div><div><br></div><div>The initial impetus was set out in a radar (<a>rdar://17630570</a>) I sent fairly early on that didn’t receive a response, so I started a <a href="http://permalink.gmane.org/gmane.comp.lang.swift.evolution/1378" target="_blank">swift-evolution</a> thread discussing the basics of this proposal. It has been refined and expanded a bit to include an effort to make Swift modules explicit and updated with the feedback of that first thread. Contents of the proposal are inline and <a href="https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6" target="_blank">can also be had as a gist</a> or <a href="https://github.com/apple/swift-evolution/pull/440" target="_blank">on Github.</a></div><div><br></div><div>Cheers,</div><div><br></div><div>~Robert Widmann</div><div><br></div><div><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">Qualified Imports and Modules</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)"><li>Proposal: <a href="https://gist.github.com/CodaFi/NNNN-first-class-qualified-imports.md" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">SE-NNNN</a></li><li style="margin-top:0.25em">Authors: <a href="https://github.com/codafi" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Robert Widmann</a>, <a href="https://github.com/harlanhaskins" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Harlan Haskins</a>, <a href="https://github.com/griotspeak" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">TJ Usiyan</a></li><li style="margin-top:0.25em">Status: <span style="font-weight:600">Awaiting review</span></li><li style="margin-top:0.25em">Review manager: TBD</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)"><a href="https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#introduction" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Introduction</h2><p style="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)">We propose a complete overhaul of the qualified imports syntax and semantics and the introduction of a module system.</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)"><a href="https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#motivation" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Motivation</h2><p style="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)">Swift code is modular by default. However, it is not clear how to decompose existing modules further into submodules. In addition, it is difficult to tell how importing a module affects its export to consumers of a library. This leads many to either fake namespaces with enums, attempt to structure Swift code with modulemaps, or use a large amount of version-control submodules. All of these can be rolled into one complete package in the form of a comprehensive rethink of the qualified import system and the introduction of a module system.</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)"><a href="https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#proposed-solution" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Proposed solution</h2><p style="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)">Modules will now become an explicit part of working with canonical Swift code. The grammar and semantics of qualified imports will change completely with the addition of <em>import qualifiers</em> and <em>import directives</em>. We also introduce three new contextual keywords: <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">using</code>, <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">hiding</code>, and <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">renaming</code>, to facilitate fine-grained usage of module contents.</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)"><a href="https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#detailed-design" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Detailed design</h2><p style="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)">Qualified import syntax will be revised to the following</p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal">module-decl -> module <module-path>
import-decl -> <access-level-modifier> import <module-path> <(opt) import-directive-list>
module-path -> <identifier>
-> <identifier>.<import-path>
import-directive-list -> <import-directive>
-> <import-directive> <import-directive-list>
import-directive -> using (<identifier>, ...)
-> hiding (<identifier>, ...)
-> renaming (<identifier>, to: <identifier>, ...)</pre></div><p style="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)">This introduces the concept of an import <em>directive</em>. An import directive is a file-local modification of an imported identifier. A directive can be one of 3 operations:</p><p style="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)">1) <em>using</em>: The <em>using</em> directive is followed by a list of identifiers within the imported module that should be exposed to this file. </p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(150,152,150)">// The only visible parts of Foundation in this file are </span>
<span style="color:rgb(150,152,150)">// Date.init(), Date.hashValue, and Date.description.</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Foundation.Date</span> using (Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">init</span>(), Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(0,134,179)">hashValue</span>, Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(0,134,179)">description</span>)</pre></div><p style="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)">2) <em>hiding</em>: The <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">hiding</code> directive is followed by a list of identifiers within the imported module that should be hidden from this file.</p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(150,152,150)">// Imports all of Foundation.Date except `Date.compare()`</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Foundation.Date</span> hiding (Date<span style="color:rgb(167,29,93)">.</span>compare())</pre></div><p style="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)">3) <em>renaming</em>: The <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">renaming</code> directive is followed by a list of identifiers separated by <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">to:</code> that should be exposed to this file but renamed. </p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(150,152,150)">// Imports all of Dispatch.DispatchQueue but renames the static member </span>
<span style="color:rgb(150,152,150)">// DispatchQueue.main, to DispatchQueue.mainQueue</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Dispatch.DispatchQueue</span> renaming (DispatchQueue<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">Type</span><span style="color:rgb(167,29,93)">.</span>main to: DispatchQueue<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">Type</span><span style="color:rgb(167,29,93)">.</span>mainQueue)
<span style="color:rgb(150,152,150)">// Renaming can also rename modules. All members of UIKit have to be qualified with</span>
<span style="color:rgb(150,152,150)">// `UI` now.</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">UIKit</span> renaming (UIKit, to: UI)</pre></div><p style="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)">Import directives chain to one another and can be used to create a fine-grained module import:</p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(150,152,150)">// Imports all of Foundation except `DateFormatter` and renames `Cache` to `LRUCache`</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Foundation</span> hiding (DateFormatter) renaming (Cache to: LRUCache)
<span style="color:rgb(150,152,150)">// Imports SCNNode except SCNNode.init(mdlObject:) and renames `.description` to</span>
<span style="color:rgb(150,152,150)">// `.nodeDescription` </span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">SceneKit</span> using (SCNNode)
renaming (SCNNode<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(0,134,179)">description</span>, to: SCNNode<span style="color:rgb(167,29,93)">.</span>nodeDescription)
hiding (SCNNode<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">init</span>(mdlObject:))</pre></div><p style="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)">Directive chaining occurs left-to-right:</p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(150,152,150)">// This says to 1) Hide nothing 2) Use nothing 3) rename Int to INT. It is invalid</span>
<span style="color:rgb(150,152,150)">// because 1) We will show everything 2) Then hide everything 3) Therefore Int is unavailable, error.</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Swift</span> hiding () using () renaming (<span style="color:rgb(0,134,179)">Int</span>, to: INT)
<span style="color:rgb(150,152,150)">// This says to 1) Use Int 2) Hide String 3) rename Double to Triple. It is invalid</span>
<span style="color:rgb(150,152,150)">// because 1) Int is available 2) String is not, error. 3) Double is unavailable, error.</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Swift</span> using (<span style="color:rgb(0,134,179)">Int</span>) hiding (<span style="color:rgb(0,134,179)">String</span>) renaming (<span style="color:rgb(0,134,179)">Double</span>, to: Triple)
<span style="color:rgb(150,152,150)">// Valid. This will be merged as `using (Int)`</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Swift</span> using () using (<span style="color:rgb(0,134,179)">Int</span>)
<span style="color:rgb(150,152,150)">// Valid. This will be merged as `hiding (String, Double)`</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Swift</span> hiding (<span style="color:rgb(0,134,179)">String</span>) hiding (<span style="color:rgb(0,134,179)">Double</span>) hiding ()
<span style="color:rgb(150,152,150)">// Valid (if redundant). This will be merged as `using ()`</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Swift</span> using (<span style="color:rgb(0,134,179)">String</span>) hiding (<span style="color:rgb(0,134,179)">String</span>)</pre></div><p style="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)"></p></div></div></blockquote><div><br></div><div>I don't mean to detract from the conversation on the deeper design aspects of this proposal, but in terms of the proposed syntax I think there's opportunity for simplification. I understand the desire to use parentheses, especially to avoid taking up `to` even as a contextual keyword, but I think it is possible to improve clarity by way of some tweaks:</div><div><br></div><div>```</div><div>import Swift using Int</div><div><br></div><div>import Swift using Int as INT, Double as Triple</div><div>// there is no possible confusion with casting here,</div><div>// and the use of `as` in this context would be familiar</div><div>// for those coming from some other languages</div><div><br></div><div>import Swift using Int, Double as Triple, String as _</div><div>// poof, no more String</div><div>```</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div><p style="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)">Module scope is delimited by the keyword <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">module</code> followed by a fully qualified name and must occur as the first declaration in a file. For example:</p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(150,152,150)">// ./Math/Integers/Arithmetic.swift</span>
module Math<span style="color:rgb(167,29,93)">.</span>Integers<span style="color:rgb(167,29,93)">.</span>Arithmetic
<span style="color:rgb(167,29,93)">public</span> <span style="color:rgb(167,29,93)">protocol</span> _IntegerArithmetic {}
<span style="color:rgb(167,29,93)">public</span> <span style="color:rgb(167,29,93)">struct</span> _Abs {}
<span style="color:rgb(167,29,93)">@_versioned</span>
<span style="color:rgb(167,29,93)">internal</span> <span style="color:rgb(167,29,93)">func</span> <span style="color:rgb(121,93,163)">_abs</span><Args>(<span style="color:rgb(121,93,163)">_</span> <span>args</span>: Args) <span style="color:rgb(167,29,93)">-></span> (_Abs, Args) {}
<span style="color:rgb(150,152,150)">// ./Math/Integers.swift</span>
module Math<span style="color:rgb(167,29,93)">.</span>Integers
<span style="color:rgb(150,152,150)">// _abs is visible in this module and all others within the project, </span>
<span style="color:rgb(150,152,150)">// but is not exported along with it.</span>
<span style="color:rgb(167,29,93)">internal</span> <span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Math.Integers.Arithmetic</span>
<span style="color:rgb(167,29,93)">public</span> <span style="color:rgb(167,29,93)">protocol</span> IntegerArithmetic <span style="color:rgb(167,29,93)">:</span> _IntegerArithmetic, <span style="color:rgb(0,134,179)">Comparable</span> {}
<span style="color:rgb(167,29,93)">public</span> <span style="color:rgb(167,29,93)">protocol</span> SignedNumber <span style="color:rgb(167,29,93)">:</span> <span style="color:rgb(0,134,179)">Comparable</span>, ExpressibleByIntegerLiteral {}
<span style="color:rgb(150,152,150)">// Math.swift</span>
module Math
<span style="color:rgb(150,152,150)">// Exports the entire public contents of Math.Integers, but nothing in </span>
<span style="color:rgb(150,152,150)">// Math.Integers.Arithmetic.</span>
<span style="color:rgb(167,29,93)">public</span> <span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Math.Integers</span></pre></div><p style="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)">Modules names are tied to a directory structure that describes their location relative to the current module and it will now be an error to violate this rule. For example:</p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal">module <span style="color:rgb(0,134,179)">String</span> <span style="color:rgb(150,152,150)">// lives in ./String.swift</span>
module <span style="color:rgb(0,134,179)">String</span><span style="color:rgb(167,29,93)">.</span>Core <span style="color:rgb(150,152,150)">// lives in ./String/Core.swift</span>
module <span style="color:rgb(0,134,179)">String</span><span style="color:rgb(167,29,93)">.</span>Core<span style="color:rgb(167,29,93)">.</span>Internals<span style="color:rgb(167,29,93)">.</span>Do<span style="color:rgb(167,29,93)">.</span>You<span style="color:rgb(167,29,93)">.</span>Even<span style="color:rgb(167,29,93)">.</span>Write <span style="color:rgb(150,152,150)">// lives in ./String/Core/Internals/Do/You/Even/Write.swift</span></pre></div><p style="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)">Existing projects that do not adopt these rules will still retain their <em>implicit module name</em> (usually defined as the name of the framework or application that is being built) and may continue to use whatever directory structure they wish, however they may not declare any explicit modules.</p><p style="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)">This proposal also solves the problem of module <em>export</em>. A module that is imported without an access level modifier will default to 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">internal</code> import per usual. However, when it is useful to fully expose the public content of submodules to a client, a <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">public</code> modifier can be used. Similarly, when it is useful to access <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">internal</code> or <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">[file]private</code> APIs, but not expose them to clients, those access modifiers may be used. The rule of thumb is: Only identifiers that are at least as visible as the qualifier on the import make for valid import declarations. For example:</p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(150,152,150)">// A submodule declaring a `private` class that gets imported with </span>
<span style="color:rgb(150,152,150)">// an `internal` qualifier with a `using` directive is an invalid import </span>
<span style="color:rgb(150,152,150)">// declaration. </span>
module Foo<span style="color:rgb(167,29,93)">.</span>Bar
<span style="color:rgb(167,29,93)">private</span> <span style="color:rgb(167,29,93)">class</span> PrivateThing {}
module Foo
<span style="color:rgb(150,152,150)">// Error: PrivateThing not visible, use `private import`</span>
<span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Foo.Bar</span> using (PrivateThing) </pre></div><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(150,152,150)">// However, a submodule declaring a `public` struct that gets imported with </span>
<span style="color:rgb(150,152,150)">// an `private` qualifier is a valid import declaration.</span>
module Foo<span style="color:rgb(167,29,93)">.</span>Bar
<span style="color:rgb(167,29,93)">public</span> <span style="color:rgb(167,29,93)">class</span> PublicThing {}
module Foo
<span style="color:rgb(150,152,150)">// All good! Foo can see Foo.Bar.PrivateThing.</span>
<span style="color:rgb(167,29,93)">private</span> <span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Foo.Bar</span> using (PublicThing) </pre></div><p style="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)">Because import directives are file-local, they will never be exported along with a <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">public</code> import and will default to exporting the entire contents of the module as though you had never declared them.</p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(150,152,150)">// In this file and this file alone, the directives apply. To the user</span>
<span style="color:rgb(150,152,150)">// of this module, it is as though this declaration were simply:</span>
<span style="color:rgb(150,152,150)">// public import Foundation.Date</span>
<span style="color:rgb(167,29,93)">public</span> <span style="color:rgb(167,29,93)">import</span> <span style="color:rgb(0,134,179)">Foundation.Date</span> hiding (Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">init</span>())
renaming (Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">Type</span><span style="color:rgb(167,29,93)">.</span>distantPast,
to: Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">Type</span><span style="color:rgb(167,29,93)">.</span>letsGoLivingInThePast,
Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">Type</span><span style="color:rgb(167,29,93)">.</span>timeIntervalSinceReferenceDate,
to: Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">Type</span><span style="color:rgb(167,29,93)">.</span>startOfTheUniverse)
renaming (Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">Type</span>.<, to: Date<span style="color:rgb(167,29,93)">.</span><span style="color:rgb(167,29,93)">Type</span>.<<<<<)</pre></div><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)"><a href="https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#impact-on-existing-code" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Impact on existing code</h2><p style="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)">Existing code that is using qualified module import syntax (<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">import {func|class|typealias|class|struct|enum|protocol} <qualified-name></code>) will be deprecated. Code that is not organized into modules will remain unaffected and organized into one contiguous top-level module. However, it is strongly recommended that frameworks be decomposed and reorganized around the new module system.</p><p style="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)">As a case study, the public interface to the standard library appears to already be mostly broken down into submodules as described in <a href="https://github.com/apple/swift/blob/master/stdlib/public/core/GroupInfo.json" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">GroupInfo.json</a>.</p><p style="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)">Code that is defined in modulemaps already defines a module structure that can be imported directly into this scheme.</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)"><a href="https://gist.github.com/CodaFi/42e5e5e94d857547abc381d9a9d0afd6#alternatives-considered" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Alternatives considered</h2><p style="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)">Module export can also be placed on the <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">module</code> declaration itself. The relevant parts of the grammar that have changed are below with an example:</p><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal">module-decl -> <access-level-modifier> module <module-path>
import-decl -> import <module-path> <(opt) import-directive-list></pre></div><div style="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)"><pre style="font-family:Consolas,'Liberation Mono',Menlo,Courier,monospace;font-size:13.600000381469727px;margin-top:0px;margin-bottom:0px;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;word-break:normal"><span style="color:rgb(167,29,93)">private</span> module <span style="color:rgb(0,134,179)">String</span><span style="color:rgb(167,29,93)">.</span>Core<span style="color:rgb(167,29,93)">.</span>Internals
<span style="color:rgb(150,152,150)">// Shh, it's a secret.</span></pre></div><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">While this style makes it immediately obvious to the library author which modules are public or private, it causes the consumer problems because submodule exports are no longer explicit and are entirely ad-hoc. In the interest of enabling, for one, users of IDEs to drill into public submodules, making export local 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">import</code> seems more appropriate.</div></div></div><br>_______________________________________________<br>
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<br></blockquote></div><br></div></div>