<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=""><div class="">I’m not saying default values should be <i class="">required</i>, just that they be allowed if it makes sense. Plus, the way Array is defined, its generic parameter can always be inferred. In your example, `a` would be an array of IntergerLiteralType (which is currently typealiased to Int). However, it’s perfectly legal to define a struct for which the compiler can’t always infer all the generic parameters</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=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">struct</span> Foo <T, U> {</div><div style="margin: 0px; line-height: normal;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">var</span> value: <span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">T</span></div><div style="margin: 0px; line-height: normal;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">var</span> opt2ndValue: <span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">U</span>?</div><div style="margin: 0px; line-height: normal;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">init</span>(<span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">_</span> value: <span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">T</span>, opt2ndValue: <span style="font-variant-ligatures: no-common-ligatures; color: #703daa" class="">U</span>? = <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">nil</span>) {</div><div style="margin: 0px; line-height: normal;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span>.<span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">value</span> = value</div><div style="margin: 0px; line-height: normal;" class=""> <span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">self</span>.<span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">opt2ndValue</span> = opt2ndValue</div><div style="margin: 0px; line-height: normal;" class=""> }</div><div style="margin: 0px; line-height: normal;" class="">}</div></div><div class="">In which case, the following code won’t compile:</div><div class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-family: Menlo; font-size: 11px; color: rgb(187, 44, 162);" class="">let</span><font face="Menlo" class=""><span style="font-size: 11px;" class=""> foo = </span></font><font face="Menlo" class=""><font color="#4f8187" class=""><span style="font-size: 11px;" class="">Foo</span></font><span style="font-size: 11px;" class="">(</span></font><span style="color: rgb(79, 129, 135); font-family: Menlo; font-size: 11px;" class="">bar</span><span style="font-size: 11px; font-family: Menlo;" class="">)</span></div></div><div class="">because <span style="color: rgb(112, 61, 170); font-family: Menlo; font-size: 11px;" class="">U</span> can’t be inferred. The current workaround:</div><div class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-family: Menlo; font-size: 11px; color: rgb(187, 44, 162);" class="">let</span><font face="Menlo" class=""><span style="font-size: 11px;" class=""> foo = </span></font><font face="Menlo" class=""><span style="font-size: 11px;" class=""><font color="#4f8187" class="">Foo</font><Int, Whatever></span><span style="font-size: 11px;" class="">(</span></font><span style="color: rgb(79, 129, 135); font-family: Menlo; font-size: 11px;" class="">bar</span><span style="font-size: 11px; font-family: Menlo;" class="">)</span></div></div><div class="">requires you to specify <i class="">all</i> the types, which means that <span style="color: rgb(79, 129, 135); font-family: Menlo; font-size: 11px;" class="">bar</span> cannot be an inferred type, because this isn’t valid:</div><div class=""><div style="margin: 0px; font-size: 11px; line-height: normal; font-family: Menlo; color: rgb(187, 44, 162);" class="">let<font face="Menlo" class=""> foo = </font><font face="Menlo" class=""><font color="#4f8187" class="">Foo</font></font><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class=""><</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">bar</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">.</span>dynamicType<span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">, </span><span style="color: rgb(0, 0, 0);" class="">Whatever</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">>(</span><span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">bar</span><span style="font-variant-ligatures: no-common-ligatures; color: #000000" class="">)</span></div></div><div class=""><br class=""></div><div class="">Default values for generic parameters let you maintain type inference, <i class="">if</i> it would make sense in your case. If it doesn’t, then don’t provide one.</div><div class=""><br class="webkit-block-placeholder"></div><div class="">
- Dave Sweeris
</div>
<br class=""><div><blockquote type="cite" class=""><div class="">On Jan 25, 2016, at 01:00, Howard Lovatt <<a href="mailto:howard.lovatt@gmail.com" class="">howard.lovatt@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="content-type" content="text/html; charset=utf-8" class=""><div dir="auto" class=""><div class="">+1 for labels, I think generics are special arguments to `inits` and therefore labels make sense to me.</div><div class=""><br class=""></div><div class="">-1 for default values, the value is inferred if not specifically specified. What would:</div><div class=""><br class=""></div><div class=""> let a = [1]</div><div class=""><br class=""></div><div class="">be? An `Int` array or an array of whatever the default generic type for an array is?<br class=""><br class="">Sent from my iPad</div><div class=""><br class="">On 24 Jan 2016, at 7:38 AM, David Sweeris via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class="">The title seems fairly self-explanatory. Does anyone else think this could be useful?<div class=""><div style="margin: 0px; line-height: normal;" class=""><span style="color: rgb(187, 44, 162); font-family: Menlo; font-size: 11px;" class="">struct</span><span style="font-family: Menlo; font-size: 11px;" class=""> True : </span><font color="#703daa" face="Menlo" class=""><span style="font-size: 11px;" class="">BooleanType</span></font><font face="Menlo" class=""><span style="font-size: 11px;" class=""> {…} </span></font><font color="#008400" face="Menlo" class=""><span style="font-size: 11px;" class="">// Just part of the example… n</span></font><span style="font-size: 11px; color: rgb(0, 132, 0); font-family: Menlo;" class="">ot in the proposal (although I do like it)</span></div><div style="margin: 0px; line-height: normal;" class=""><span style="color: rgb(187, 44, 162); font-family: Menlo; font-size: 11px;" class="">struct</span><span style="font-family: Menlo; font-size: 11px;" class=""> False : </span><font color="#703daa" face="Menlo" class=""><span style="font-size: 11px;" class="">BooleanType</span></font><font face="Menlo" class=""><span style="font-size: 11px;" class=""> {…} </span></font><font color="#008400" face="Menlo" class=""><span style="font-size: 11px;" class="">// Same</span></font></div></div><div style="margin: 0px; line-height: normal;" class=""><span style="color: rgb(0, 132, 0); font-family: Menlo; font-size: 11px;" class="">// This is where the actual idea starts</span></div><div class=""><div style="margin: 0px; line-height: normal;" class=""><div style="font-size: 11px; font-family: Menlo; margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">struct</span> BigInt <BaseType: T = <span style="color: rgb(112, 61, 170);" class="">Int</span>, CanEqualZero: U = <span style="color: rgb(79, 129, 135);" class="">Yes </span><span style="color: rgb(187, 44, 162);" class="">where</span> T: IntegerArithmeticType, U: BooleanType> {…}</div><div style="margin: 0px; line-height: normal;" class=""><br class=""></div><div style="margin: 0px; line-height: normal;" class="">The first parameter label could be skipped (or not), depending on whatever the rules for functions parameter labels ends up being (either way, they should be the same IMHO). Then variables could be declared like this:</div><div style="margin: 0px; line-height: normal;" class=""><div style="font-family: Menlo; font-size: 11px; margin: 0px; line-height: normal;" class=""><span style="font-variant-ligatures: no-common-ligatures; color: #bb2ca2" class="">let</span> foo = <span style="font-variant-ligatures: no-common-ligatures; color: #4f8187" class="">BigInt</span>()<span class="Apple-tab-span" style="white-space:pre"> </span> <span style="color: rgb(0, 132, 0);" class="">// BigInt<Int, No>()</span></div><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""><font face="Menlo" style="font-size: 11px;" class=""><span style="color: rgb(187, 44, 162);" class="">let</span><font class=""> bar = </font><span style="color: rgb(79, 129, 135);" class="">BigInt</span><font class=""><Int32>() </font><span style="color: rgb(0, 132, 0);" class="">// For when your data will be processed on a 32-bit platform or something</span></font></div></div></div><div class=""><div style="margin: 0px; line-height: normal;" class=""><div style="margin: 0px; line-height: normal;" class=""><span style="font-family: Menlo; font-size: 11px; color: rgb(187, 44, 162);" class="">let</span><font face="Menlo" class=""><span style="font-size: 11px;" class=""> divisor = </span></font><span style="font-family: Menlo; font-size: 11px; color: rgb(79, 129, 135);" class="">BigInt</span><font face="Menlo" class=""><span style="font-size: 11px;" class=""><CanEqualZero: </span></font><span style="color: rgb(79, 129, 135); font-family: Menlo; font-size: 11px;" class="">False</span><font face="Menlo" class=""><span style="font-size: 11px;" class="">>()</span></font></div><div style="font-family: Menlo; font-size: 11px;" class=""><br class=""></div></div></div><div class="">(The obvious follow-up suggestion is to then allow a generic type’s definition to change based on the results of logical operations performed purely on the types that are passed in, but I think that’s getting into “macro system” territory, and should probably be its own thing.)</div><div class=""><br class=""></div><div class="">Anyway, thoughts?</div></div></div><br class=""><div class="">
- Dave Sweeris
</div>
<br class=""></div></blockquote><blockquote type="cite" class=""><div class=""><span class="">_______________________________________________</span><br class=""><span class="">swift-evolution mailing list</span><br class=""><span class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a></span><br class=""><span class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br class=""></div></blockquote></div></div></blockquote></div><br class=""></div></body></html>