<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">I agree that the compiler should be able to use a function with default values for protocol conformance.<br class=""><div class="">
<br class="Apple-interchange-newline"><span style="color: rgb(0, 0, 0); font-family: 'Lucida Grande'; font-size: 12px; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; orphans: 2; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; display: inline !important; float: none;" class="">Félix</span>
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<br class=""><div><blockquote type="cite" class=""><div class="">Le 17 janv. 2016 à 11:52:06, J. Cheyo Jimenez via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> a écrit :</div><br class="Apple-interchange-newline"><div class="">This is very interesting. The first case seems like a bug because the compiler should not let you define that function(). <div class=""><br class=""></div><div class="">Do you have any actual examples when you would need to conform to the same function name but with different signatures? <br class=""><div class=""><br class="">On Sunday, January 17, 2016, 肇鑫 via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr" class=""><div class="gmail_default" style="font-family:georgia,serif">This proposal is the summary of the previous protocol function default value proposal and some of my new thinkings all together.</div><div class="gmail_default" style="font-family:georgia,serif"><br class=""></div><div class="gmail_default" style="font-family:georgia,serif">Currently the compiler doesn't stop you defining two functions like:</div><div class="gmail_default" style="font-family:georgia,serif"><br class=""></div><div class="gmail_default"><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="color:rgb(187,44,162)" class="">func</span> printSomething(something:<span style="color:rgb(112,61,170)" class="">String</span> = <span style="color:rgb(209,47,27)" class="">"some thing"</span>) {</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""> <span style="color:rgb(61,29,129)" class="">print</span>(something)</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class="">}</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal; min-height: 13px;" class=""><br class=""></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="color:rgb(187,44,162)" class="">func</span> printSomething() {</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal; color: rgb(209, 47, 27);" class=""><span style="" class=""> </span><span style="color:rgb(61,29,129)" class="">print</span><span style="" class="">(</span>"some thing!"<span style="" class="">)</span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class="">}</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class="">However, when you call it, an error arises.</font></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class=""><br class=""></font></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(0, 132, 0);" class=""><span style="" class="">printSomething() </span>// Ambiguous use of 'printSomething'</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-family:georgia,serif" class="">You may say just remove the function that has no argument. But protocol needs it.</span><br class=""></div><div style="margin: 0px; line-height: normal;" class=""><span style="font-family:georgia,serif" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class="">protocol<span style="" class=""> A {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething(something:<span style="color:rgb(112,61,170)" class="">String</span>)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething()</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="color:rgb(187,44,162)" class="">struct</span> Foo:<span style="color:rgb(79,129,135)" class="">A</span> {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething(something:<span style="color:rgb(112,61,170)" class="">String</span>) {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(61,29,129)" class="">print</span>(something)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;min-height:13px" class=""> <br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething() {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(49, 89, 93);" class=""><span style="" class=""> </span><span style="color:rgb(187,44,162)" class="">self</span><span style="" class="">.</span>printSomething<span style="" class="">(</span><span style="color:rgb(209,47,27)" class="">"some thing"</span><span style="" class="">)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;line-height:normal" class="">
</p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class="">If you do't define the no-argument function in protocol A. You can not use the function by (Foo() as A).printSomething().</span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class="">As we all know, a function with default values, can rewrite to two or more equivalent functions. For example,</font></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class=""><br class=""></font></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="color:rgb(187,44,162)" class="">struct</span> Bar {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> add(int1:<span style="color:rgb(112,61,170)" class="">Int</span> = <span style="color:rgb(39,42,216)" class="">1</span>, int2:<span style="color:rgb(112,61,170)" class="">Int</span> = <span style="color:rgb(39,42,216)" class="">2</span>, int3:<span style="color:rgb(112,61,170)" class="">Int</span> = <span style="color:rgb(39,42,216)" class="">3</span>) {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(61,29,129)" class="">print</span>(int1 + int2 + int3)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo" class="">
</p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class="">is equivalent to </span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="color:rgb(187,44,162)" class="">struct</span> Bar {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> add(int1:<span style="color:rgb(112,61,170)" class="">Int</span>, int2:<span style="color:rgb(112,61,170)" class="">Int</span>, int3:<span style="color:rgb(112,61,170)" class="">Int</span>) {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(61,29,129)" class="">print</span>(int1 + int2 + int3)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;min-height:13px" class=""> <br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> add() {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">self</span>.<span style="color:rgb(49,89,93)" class="">add</span>(<span style="color:rgb(39,42,216)" class="">1</span>, int2: <span style="color:rgb(39,42,216)" class="">2</span>, int3: <span style="color:rgb(39,42,216)" class="">3</span>)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;min-height:13px" class=""> <br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> add(int1:<span style="color:rgb(112,61,170)" class="">Int</span>) {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">self</span>.<span style="color:rgb(49,89,93)" class="">add</span>(int1, int2: <span style="color:rgb(39,42,216)" class="">2</span>, int3: <span style="color:rgb(39,42,216)" class="">3</span>)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;min-height:13px" class=""> <br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> add(int1:<span style="color:rgb(112,61,170)" class="">Int</span>, int2:<span style="color:rgb(112,61,170)" class="">Int</span>) {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">self</span>.<span style="color:rgb(49,89,93)" class="">add</span>(int1, int2: int2, int3: <span style="color:rgb(39,42,216)" class="">3</span>)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="font-family:Menlo;margin:0px;font-size:11px;line-height:normal" class="">
</p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class="">So my proposal is let compiler or pre-compiler to generate the code internally, without changing the original code, base on the functions that have default values.</font></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class=""><br class=""></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class="">Then we need not to define multiple functions in a protocol when we need function with default values.</font></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class=""><br class=""></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class="">new code:</font></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class=""><br class=""></font></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class="">protocol<span style="" class=""> A {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething(something:<span style="color:rgb(112,61,170)" class="">String</span>)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="color:rgb(187,44,162)" class="">struct</span> Foo:<span style="color:rgb(79,129,135)" class="">A</span> {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething(something:<span style="color:rgb(112,61,170)" class="">String</span> = <span style="color:rgb(209,47,27)" class="">"some thing"</span>) {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(61,29,129)" class="">print</span>(something)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;line-height:normal" class="">
</p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class=""><br class=""></font></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class=""><br class=""></font></div><div style="margin: 0px; line-height: normal;" class="">If we don't want to change our previous code, we may also need to introduce another keyword defaultValue. This keyword is used only in a protocol to restrict if a function's argument can have a default value. If a function use it, but the implementation doesn't give a default value, or vice versa, an error arises.</div><div style="margin: 0px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class="">new code:</div><div style="margin: 0px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class="">protocol<span style="" class=""> A {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething(something:<span style="color:rgb(112,61,170)" class="">String</span> = defaultValue)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="color:rgb(187,44,162)" class="">struct</span> Foo:<span style="color:rgb(79,129,135)" class="">A</span> {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething(something:<span style="color:rgb(112,61,170)" class="">String</span> = <span style="color:rgb(209,47,27)" class="">"some thing"</span>) {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(61,29,129)" class="">print</span>(something)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;line-height:normal" class=""></p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class="">This keyword is useful. With it, you can still use Swift in old way. Which means you need not to change code like below if you don't want to.</span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class="">old code:</span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class="">protocol<span style="" class=""> A {</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething(something:<span style="color:rgb(112,61,170)" class="">String</span>)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething()</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; min-height: 13px;" class=""><br class=""></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""><span style="color:rgb(187,44,162)" class="">struct</span> Foo:<span style="color:rgb(79,129,135)" class="">A</span> {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething(something:<span style="color:rgb(112,61,170)" class="">String</span>) {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(61,29,129)" class="">print</span>(something)</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;min-height:13px" class=""> <br class="webkit-block-placeholder"></p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> <span style="color:rgb(187,44,162)" class="">func</span> printSomething() {</div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(49, 89, 93);" class=""><span style="" class=""> </span><span style="color:rgb(187,44,162)" class="">self</span><span style="" class="">.</span>printSomething<span style="" class="">(</span><span style="color:rgb(209,47,27)" class="">"some thing"</span><span style="" class="">)</span></div><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class=""> }</div><p style="margin:0px;line-height:normal" class=""></p><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo;" class="">}</div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="margin: 0px; line-height: normal;" class=""><font face="georgia, serif" class="">But if you want to write new code. You can just write it in the new way, enjoining the simpler and clearer.</font></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class="">zhaoxin</span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div><div style="font-family: Menlo; margin: 0px; font-size: 11px; line-height: normal;" class=""><span style="font-family:georgia,serif;font-size:small" class=""><br class=""></span></div></div></div>
</blockquote></div></div>
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