<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class=""><br class=""></div><div class="">Everyone loves this syntax:</div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> pos = [1, -2, 3].</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">map</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">abs</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; line-height: normal;" class=""><br class=""></div></div><div style="font-family: Helvetica; font-size: 14px;" class="">This syntax not so much:</div><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> neg = [1, -2, 3].<span style="color: rgb(52, 149, 175);" class="">map</span>({ -<span style="color: rgb(52, 149, 175);" class="">abs</span>($0) })</span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div></div><div style="font-family: Helvetica; font-size: 14px;" class="">For single-statement closures, ordered parameters could be referenced in an autoclosure-like way using a placeholder for the parameter:</div><div style="font-family: Helvetica; font-size: 14px;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span> neg = [1, -2, 3].<span style="color: rgb(52, 149, 175);" class="">map</span>(-<span style="color: rgb(52, 149, 175);" class="">abs</span>(<span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">_</span>))</div><div class=""><br class=""></div></div></div></div></div></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class="">The behavior would be the same as the current $0, $1, ... shorthand argument names to inline closures except that parameter re-ordering wouldn't be allowed (the first instance of _ would be $0, the second would be $1, etc). So t</span>he following three lines would all be compiled the same:</div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><div class=""><br class=""></div></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><div style="font-family: Menlo; font-size: 11px; margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> reversed = words.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">sort</span><span style="font-variant-ligatures: no-common-ligatures;" class="">( { $0 > $1 } )</span></div><div style="font-family: Menlo; font-size: 11px; margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> reversed = <span style="font-variant-ligatures: no-common-ligatures;" class="">words.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">sort</span>(</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">_</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> > </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">_</span><span style="font-variant-ligatures: no-common-ligatures;" class="">)</span></div><div style="font-family: Menlo; font-size: 11px; margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> reversed = words.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">sort</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(>)</span></div><div class=""><br class=""></div></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class="">As with autoclosures, noescape rules would be enforced since there wouldn't be any way to specify that self is weak or unowned. So while the following requires use of self to make capture semantics explicit:</span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> words.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">lazy</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">filter</span><span style="font-variant-ligatures: no-common-ligatures" class="">({ $0.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">hashValue</span><span style="font-variant-ligatures: no-common-ligatures" class=""> == </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">hashValue</span><span style="font-variant-ligatures: no-common-ligatures" class=""> })</span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div></span></div><div class="">These would both raise errors:</div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> words.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">lazy</span><span style="font-variant-ligatures: no-common-ligatures;" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">filter</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(_.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">hashValue</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> == </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">hashValue</span><span style="font-variant-ligatures: no-common-ligatures;" class="">)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> words.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">lazy</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">filter</span><span style="font-variant-ligatures: no-common-ligatures" class="">(_.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">hashValue</span><span style="font-variant-ligatures: no-common-ligatures" class=""> == </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">self</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">hashValue</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div class=""><br class=""></div></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class="">Nested closures would also behave the same as with dollar-shorthand:</span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> words = [</span><span style="font-variant-ligatures: no-common-ligatures; color: #b4261a" class="">"abc"</span><span style="font-variant-ligatures: no-common-ligatures" class="">, </span><span style="font-variant-ligatures: no-common-ligatures; color: #b4261a" class="">"def"</span><span style="font-variant-ligatures: no-common-ligatures" class="">, </span><span style="font-variant-ligatures: no-common-ligatures; color: #b4261a" class="">"hij"</span><span style="font-variant-ligatures: no-common-ligatures" class="">]</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ascii = words.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">flatMap</span><span style="font-variant-ligatures: no-common-ligatures" class="">({ $0.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">unicodeScalars</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">filter</span><span style="font-variant-ligatures: no-common-ligatures" class="">({ $0.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">isASCII</span><span style="font-variant-ligatures: no-common-ligatures" class=""> }) })</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> ascii = words.flatMap(</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">.<span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">unicodeScalars</span><span class="" style="font-variant-ligatures: no-common-ligatures;">.</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">filter</span>(</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">.isASCII))</span></div><div class=""><br class=""></div></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class="">Another example:</span></div><div class=""><br class=""></div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span class="" style="font-variant-ligatures: no-common-ligatures;"> </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">let</span><span class="" style="font-variant-ligatures: no-common-ligatures;"> words: [</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);">String</span><span class="" style="font-variant-ligatures: no-common-ligatures;">?] = [</span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(180, 38, 26);">"Hey"</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(180, 38, 26);">"you"</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);">nil</span><span class="" style="font-variant-ligatures: no-common-ligatures;">, </span><span class="" style="font-variant-ligatures: no-common-ligatures; color: rgb(180, 38, 26);">"guys"</span><span class="" style="font-variant-ligatures: no-common-ligatures;">]</span></div></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><div style="font-family: Helvetica; font-size: 14px;" class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> exclaim = words.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">flatMap</span><span style="font-variant-ligatures: no-common-ligatures;" class="">({ $0 }).</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">map</span><span style="font-variant-ligatures: no-common-ligatures;" class="">({ $0.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">uppercaseString</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> }).</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">reduce</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(180, 38, 26);" class="">""</span><span style="font-variant-ligatures: no-common-ligatures;" class="">, combine: { $0+</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(180, 38, 26);" class="">"! "</span><span style="font-variant-ligatures: no-common-ligatures;" class="">+$1 })</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">let</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> exclaim = words.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">flatMap</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">_</span><span style="font-variant-ligatures: no-common-ligatures;" class="">).</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">map</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">_</span><span style="font-variant-ligatures: no-common-ligatures;" class="">.uppercaseString).reduce(</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(180, 38, 26);" class="">""</span><span style="font-variant-ligatures: no-common-ligatures;" class="">, combine: </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">_</span><span style="font-variant-ligatures: no-common-ligatures;" class="">+</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(180, 38, 26);" class="">"! "</span><span style="font-variant-ligatures: no-common-ligatures;" class="">+</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">_</span><span style="font-variant-ligatures: no-common-ligatures;" class="">)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""><br class=""></span></div></div></div><div class=""><br class=""></div><div class="">Why underscore and not another character like a lone "$" or "."? The meaning of the underscore character as an anonymous ordered placeholder would be consistent with other usages throughout the Swift language. Examples:</div></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> (</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">, </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">two</span><span style="font-variant-ligatures: no-common-ligatures" class="">, </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">) = (1, 2.0, </span><span style="font-variant-ligatures: no-common-ligatures; color: #b4261a" class="">"Three"</span><span style="font-variant-ligatures: no-common-ligatures" class="">) // anonymous tuple property</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures;" class="">words.</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(52, 149, 175);" class="">reduce</span><span style="font-variant-ligatures: no-common-ligatures;" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(180, 38, 26);" class="">""</span><span style="font-variant-ligatures: no-common-ligatures;" class="">, combine: { (x, </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">_</span><span style="font-variant-ligatures: no-common-ligatures;" class="">) </span><span style="font-variant-ligatures: no-common-ligatures; color: rgb(4, 51, 255);" class="">in</span><span style="font-variant-ligatures: no-common-ligatures;" class=""> x }) // anonymous closure parameter</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">let</span><span style="font-variant-ligatures: no-common-ligatures" class=""> advancer = </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">Int</span><span style="font-variant-ligatures: no-common-ligatures" class="">.</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">advancedBy</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">:limit:) // anonymous function argument</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">switch</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #b4261a" class="">"X"</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">as</span><span style="font-variant-ligatures: no-common-ligatures" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">String?</span><span style="font-variant-ligatures: no-common-ligatures" class=""> {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> .</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">Some</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">_</span><span style="font-variant-ligatures: no-common-ligatures" class="">): </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">print</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #b4261a" class="">"something"</span><span style="font-variant-ligatures: no-common-ligatures" class="">) // anonymous enum value</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures;" class=""> </span><span style="font-variant-ligatures: no-common-ligatures; color: #0433ff" class="">case</span><span style="font-variant-ligatures: no-common-ligatures" class=""> .</span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">None</span><span style="font-variant-ligatures: no-common-ligatures" class="">: </span><span style="font-variant-ligatures: no-common-ligatures; color: #3495af" class="">print</span><span style="font-variant-ligatures: no-common-ligatures" class="">(</span><span style="font-variant-ligatures: no-common-ligatures; color: #b4261a" class="">"nothing"</span><span style="font-variant-ligatures: no-common-ligatures" class="">)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="font-variant-ligatures: no-common-ligatures" class=""> }</span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures" class=""><br class=""></span></div></span></div><div class=""><span style="font-variant-ligatures: no-common-ligatures;" class="">And </span>since underscore currently isn't allowed on the right-hand side of an expression, this syntax enhancement shouldn't break any existing code. Lastly, this same syntax for anonymous arguments is used in Scala, so it would already be familiar to a large developer base.</div><div class=""><br class=""></div><div class="">Any yeas or nays?</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>-Marc</div><div class=""><br class=""></div></body></html>