<div>I like the ~> operator, but not := operator. It makes the language inconsistent. Then we should allow using it without "if" just like this:</div><div>mylet := "hey there"</div><div><br></div><div>I think we should keep let as it was and avoid :=</div><div><br></div><div>P.S.: it also looks too much Pascal-ish :)</div><div><br><div class="gmail_quote"><div>On Tue, 28 Feb 2017 at 21:02 Erica Sadun via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br></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" class="gmail_msg"><div style="word-wrap:break-word" class="gmail_msg">The following draft proposal addresses one matter of substance (eliminating edge case errors by adopting at-site conditional binding) and one of style (using the pattern match operator consistently). Its discussion was deferred from Phase 1 and remains in a fairly early stage. Your feedback will help me decide whether this is a proposal I want to keep developing or one that I should set aside and focus on other matters. Thank you. -- E<div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">The work-in-progress gist is here: <a href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c" class="gmail_msg" target="_blank">https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c</a> </div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><h1 style="box-sizing:border-box;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',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255);margin-top:0px!important" class="gmail_msg">Simplifying case syntax</h1><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg"><li style="box-sizing:border-box" class="gmail_msg">Proposal: TBD</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg">Author: <a href="https://github.com/erica" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" class="gmail_msg" target="_blank">Erica Sadun</a></li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg">Status: TBD</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg">Review manager: TBD</li></ul><h2 style="box-sizing:border-box;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',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-introduction" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#introduction" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Introduction</h2><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">This proposal re-architects case syntax grammar to reduce potential errors and simplify unwrapping enumerations. </p><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Swift-evolution thread: <a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20161024/tbd.html" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" class="gmail_msg" target="_blank">[Pitch] Reimagining <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">guard case</code>/<code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case</code></a></p><h2 style="box-sizing:border-box;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',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-motivation" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#motivation" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Motivation</h2><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">In its current design, Swift case binding suffers from two weaknesses.</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg"><li style="box-sizing:border-box" class="gmail_msg">Mixed external and internal <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">let</code>/<code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">var</code> binding may introduce errors from uncommon edge cases.</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg">Real-world users may not consider the parallel construction between <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case</code>/<code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">guard case</code> with <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">switch</code>statements or naturally connect the two layouts.</li></ul><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-internal-case-binding" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#internal-case-binding" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Internal Case Binding</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">When pattern matching, it's common to bind a variable or constant. It's uncommon but legal to use a bound value as an argument. Adopting an "always explicit, always within the parentheses" rule adds consistency and safety to Swift. </p><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Consider the following enumeration and values:</p><div class="m_4134157978096849346highlight m_4134157978096849346highlight-source-swift gmail_msg" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:SFMono-Regular,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" class="gmail_msg"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> An enum with one, two, or three associated values</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">enum</span> <span class="m_4134157978096849346pl-en gmail_msg" style="box-sizing:border-box;color:rgb(121,93,163)">Value</span><<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">T</span>> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">one</span>(T), <span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">two</span>(T, T), <span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">three</span>(T, T, T) }
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> An example with two associated values</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> example2<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span> <span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">Value</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)"><</span><span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">Character</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">></span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">two</span>(<span class="m_4134157978096849346pl-s gmail_msg" style="box-sizing:border-box;color:rgb(24,54,145)"><span class="m_4134157978096849346pl-pds gmail_msg" style="box-sizing:border-box">"</span>a<span class="m_4134157978096849346pl-pds gmail_msg" style="box-sizing:border-box">"</span></span>, <span class="m_4134157978096849346pl-s gmail_msg" style="box-sizing:border-box;color:rgb(24,54,145)"><span class="m_4134157978096849346pl-pds gmail_msg" style="box-sizing:border-box">"</span>b<span class="m_4134157978096849346pl-pds gmail_msg" style="box-sizing:border-box">"</span></span>)
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> A bound symbol</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> oldValue <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> <span class="m_4134157978096849346pl-s gmail_msg" style="box-sizing:border-box;color:rgb(24,54,145)"><span class="m_4134157978096849346pl-pds gmail_msg" style="box-sizing:border-box">"</span>x<span class="m_4134157978096849346pl-pds gmail_msg" style="box-sizing:border-box">"</span></span></pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">This code's goal is to conditionally bind <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">newValue</code> and pattern match the value stored in the <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">oldValue</code> symbol. The first example succeeds. The second example compiles and runs but does not match the coder's intent. Using an external <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">let</code>creates a new <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">oldValue</code> shadow instead of pattern matching <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">oldValue</code>'s stored value.</p><pre style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg"><code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">// Safe
if case .two(let newValue, oldValue) = example2 {
...
}
// Syntactically legal but incorrect
if case let .two(newValue, oldValue) = example2 {
...
}
</code></pre><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">In-parenthesis binding avoids accidental shadowing. It eliminates this class of error by adding <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">let</code> and <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">var</code> key words to each use point. This creates longer call sites but enumerations rarely contain more than three or four associated items.</p><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Adopting point-of-use binding enhances clarity and readability. Both <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case let</code> and <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case var</code> (plus <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">case var</code>and <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">case let</code>) may look like single compound keywords rather than a combination of two distinct actions to developers unfamiliar with this syntax.</p><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-pattern-matching-with-conditional-binding" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#pattern-matching-with-conditional-binding" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Pattern Matching with Conditional Binding</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Swift's <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">guard case</code> and <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case</code> align statement design with the <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">switch</code> statement, moving the matched value to the right of an equal sign.</p><div class="m_4134157978096849346highlight m_4134157978096849346highlight-source-swift gmail_msg" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:SFMono-Regular,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" class="gmail_msg"><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">switch</span> value {
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">enumeration</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> embedded)<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span>
}
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">enumeration</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> embedded) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> value</pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">The status quo for the <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">=</code> operator is iteratively built up in this fashion:</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg"><li style="box-sizing:border-box" class="gmail_msg"><code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">=</code> performs assignment</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg"><code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">let x =</code> performs binding</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg"><code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if let x =</code> performs conditional binding on optionals</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg"><code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case .foo(let x) =</code> performs conditional binding on enumerations <em style="box-sizing:border-box" class="gmail_msg">and</em> applies pattern matching</li></ul><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Using <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case</code>/<code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">guard case</code> in the absense of conditional binding duplicates basic pattern matching with less obvious meaning. These two statements are functionally identical:</p><div class="m_4134157978096849346highlight m_4134157978096849346highlight-source-swift gmail_msg" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:SFMono-Regular,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" class="gmail_msg"><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> range <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> myValue { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> simpler</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> range <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> myValue { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> confusing</span></pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Issues with the current design include:</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg"><li style="box-sizing:border-box" class="gmail_msg"><code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">guard case</code> and <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case</code> look like standard non-conditional assignment statements but they are <em style="box-sizing:border-box" class="gmail_msg">not</em> assignment statements. Using the assignment operator violates the <a href="https://en.wikipedia.org/wiki/Principle_of_least_astonishment" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none" class="gmail_msg" target="_blank">principle of least astonishment</a>.<br style="box-sizing:border-box" class="gmail_msg"></li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg">In <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">switch</code>, a <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">case</code> is followed by a colon, not an assignment operator.</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg">Swift <em style="box-sizing:border-box" class="gmail_msg">has</em> a pattern matching operator (<code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">~=</code>) but does not use it here.</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg"><code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">case</code> syntax is wordy. The statement includes <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">case</code>, <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">=</code>, and optionally <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">let</code>/<code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">var</code> conditional binding. Design alternatives could streamline this syntax, enhance clarity, and introduce a more concise format.</li></ul><h2 style="box-sizing:border-box;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',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-detailed-design" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#detailed-design" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Detailed Design</h2><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">This proposal adopts point-of-use conditional binding and recommends one of the following designs. A successful design will replace the current syntax with a simpler grammar that prioritizes pattern matching and support conditional binding.</p><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-design-1-using-the-pattern-matching-operator" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#design-1-using-the-pattern-matching-operator" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Design 1: Using the Pattern Matching Operator</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">This design drops the <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">case</code> keyword and replaces <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">=</code> with <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">~=</code>. The results look like this, showcasing a variety of <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">let</code>placement, variable binding, and optional sugar alternatives.</p><div class="m_4134157978096849346highlight m_4134157978096849346highlight-source-swift gmail_msg" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:SFMono-Regular,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" class="gmail_msg"><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> value) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> result <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> value) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> result <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> value) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> result { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> value) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> result { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> anOptional <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> anOptional { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }</pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">In this design:</p><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg"><li style="box-sizing:border-box" class="gmail_msg">The <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">case</code> keyword is subsumed into the (existing) pattern matching operator</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg">The statements adopt the existing <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if-let</code>/<code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if var</code> and <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">guard-let</code>/<code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">guard var</code> syntax, including <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">Optional</code>syntactic sugar.</li></ul><div class="m_4134157978096849346highlight m_4134157978096849346highlight-source-swift gmail_msg" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:SFMono-Regular,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" class="gmail_msg"><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> current</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span>
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> would be removed</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> x<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> anOptional { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> proposed replacement for `if case`</span></pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Pattern matching without conditional binding simplifies to a standalone Boolean condition clause. On adopting this syntax, the two identical range tests naturally unify to this single version:</p><div class="m_4134157978096849346highlight m_4134157978096849346highlight-source-swift gmail_msg" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:SFMono-Regular,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" class="gmail_msg"><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> range <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> myValue { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> before</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">case</span> range <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> myValue { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> before</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span>
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> range <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">~=</span> myValue { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> after</span></pre></div><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-design-2-using-a-declare-and-assign-operator" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#design-2-using-a-declare-and-assign-operator" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Design 2: Using a Declare and Assign Operator</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">This design introduces new <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">:=</code> "declare and assign" operator. This operator eliminates the need for explicit <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">let</code>, although the keyword is allowed and most house style guides would recommend its use:</p><div class="m_4134157978096849346highlight m_4134157978096849346highlight-source-swift gmail_msg" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:SFMono-Regular,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" class="gmail_msg"><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(value) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> result <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> value) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> result <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(value) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> result { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> value) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> result { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> }
<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> value<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> newly legal, although unnecessary</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> value<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> newly legal, although unnecessary</span></pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Assignments to variables require the <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">var</code> keyword, enabling coders to clarify the distinct roles in mix-and-match pattern matching:</p><div class="m_4134157978096849346highlight m_4134157978096849346highlight-source-swift gmail_msg" style="box-sizing:border-box;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)"><pre style="box-sizing:border-box;font-family:SFMono-Regular,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" class="gmail_msg"><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">pair</span>(value1, <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> value2) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> result <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> implied let</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">pair</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">let</span> value1, <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> value2) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> result <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> explicit let</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">if</span> .<span class="m_4134157978096849346pl-c1 gmail_msg" style="box-sizing:border-box;color:rgb(0,134,179)">success</span>(<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> value) <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> result { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> variable assignment</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> x<span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">?</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> variable assignment</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> x <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> simpler variable assignment</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">var</span> x <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> even simpler (current) variable assignment</span>
<span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"></span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">guard</span> x <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">:</span><span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">=</span> anOptional <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">else</span> { <span class="m_4134157978096849346pl-k gmail_msg" style="box-sizing:border-box;color:rgb(167,29,93)">...</span> } <span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box;color:rgb(150,152,150)"><span class="m_4134157978096849346pl-c gmail_msg" style="box-sizing:border-box">//</span> new constant assignment</span></pre></div><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Adopting this syntax provides more natural results for binding associated enumeration variables.</p><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-excluded-from-this-proposal" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#excluded-from-this-proposal" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Excluded from this proposal</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">This proposal does not address <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">switch case</code> or <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">for case</code> beyond internal binding requirements.</p><h2 style="box-sizing:border-box;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',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-impact-on-existing-code" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#impact-on-existing-code" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Impact on Existing Code</h2><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">This proposal is breaking and would require migration. External <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">let</code> or <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">var</code> would automatically be moved by fixits into use points. Current <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">guard case</code> and <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case</code> syntax would be migrated to the new design.</p><h3 style="box-sizing:border-box;margin-top:24px;margin-bottom:16px;font-size:1.25em;line-height:1.25;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-timeline" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#timeline" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Timeline</h3><p style="box-sizing:border-box;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';font-size:16px;background-color:rgb(255,255,255)" class="gmail_msg">Although removing <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">if case</code> and <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">guard case</code> are breaking, this proposal should wait until Swift 4 Stage two to allow proper debate and consideration from the core team.</p><h2 style="box-sizing:border-box;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',Helvetica,Arial,sans-serif,'Apple Color Emoji','Segoe UI Emoji','Segoe UI Symbol';background-color:rgb(255,255,255)" class="gmail_msg"><a id="m_4134157978096849346user-content-alternatives-considered" class="m_4134157978096849346anchor gmail_msg" href="https://gist.github.com/erica/06dad9bbe1a70290fe6b89a64f73bc0c#alternatives-considered" style="box-sizing:border-box;background-color:transparent;color:rgb(64,120,192);text-decoration:none;float:left;padding-right:4px;line-height:1" target="_blank"><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u><u class="gmail_msg"></u></a>Alternatives Considered</h2><ul style="box-sizing:border-box;padding-left:2em;margin-top:0px;color:rgb(51,51,51);font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',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="gmail_msg"><li style="box-sizing:border-box" class="gmail_msg">Leaving the grammar as-is, albeit confusing</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg">Retaining <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">case</code> and replacing the equal sign with <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">~=</code> (pattern matching) or <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">:</code> (to match the switch statement).</li><li style="box-sizing:border-box;margin-top:0.25em" class="gmail_msg">Adding <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">matches</code> or <code style="box-sizing:border-box;font-family:SFMono-Regular,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="gmail_msg">is</code> as an alternative to the pattern matching operator</li></ul><div class="gmail_msg"><br class="gmail_msg"></div></div></div></div>_______________________________________________<br class="gmail_msg">
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