<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="">These are fantastic proposals! With these in place, there would be precious little to envy Haskell. <div class=""><br class=""></div><div class="">For example, regarding “counter-proposal against making generic parameters public”, the current behaviour of Swift is essentially a bug, as reported by Noah Blake (<a href="https://bugs.swift.org/browse/SR-1065" class="">https://bugs.swift.org/browse/SR-1065</a>).</div><div class=""><br class=""></div><div class="">Then there is:</div><div class=""><br class=""></div><div class=""><blockquote type="cite" class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class="">(3) Using variadic patterns (shamefully borrowing the `<font face="Menlo" class="" style="font-size: 11px;">...</font>` notation from C++ here to mean an arbitrary-length list of patterns to match or expressions to expand):</div><div class=""><br class=""></div><div class=""><div class=""><font face="Menlo" class="" style="font-size: 11px;"> extension <b class="">(T...) : Equatable where T : Equatable...</b> {</font><font face="Menlo" class="" style="font-size: 11px;">}</font></div><div class=""><font face="Menlo" class="" style="font-size: 11px;"><br class=""></font></div><div class=""><font face="Menlo" class="" style="font-size: 11px;"> func == <b class=""><T...></b>(lhs: <b class="">(T...)</b>, rhs: <b class="">(T...)</b>) -> Bool <b class="">where T : Equatable...</b> {</font><font face="Menlo" class="" style="font-size: 11px;"> </font><span class="" style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;">/* ... */</span><font face="Menlo" class="" style="font-size: 11px;"> </font><font face="Menlo" class="" style="font-size: 11px;">}</font></div></div></div></div></blockquote></div><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class=""><div class=""><div class=""><font face="Menlo" class="" style="font-size: 11px;"><br class=""></font></div><div class="">Not only that this would make certain Standard Library signatures less embarrassing, but would enable entirely new programming patterns. For example, the size of a fixed-length sequence could be type guaranteed like so:</div><div class=""><br class=""></div><div class=""><font face="Menlo" style="font-size: 12px;" class=""> let v = <b class="">Vector</b><<b class="">_2</b>,<b class="">_0</b>,<b class="">_1</b>,<b class="">_6</b>>(repeatedValue: 42)</font></div><div class=""><font face="Menlo" style="font-size: 12px;" class=""> v.<b class="">count</b> // 2016</font></div><div class=""><br class=""></div><div class="">… wehere types like <b class="">_2</b> and <b class="">_6</b> may be caseless enums:</div><div class=""><br class=""></div><div class=""><div class=""><font face="Menlo" style="font-size: 12px;" class=""> <b class="">enum</b> <b class="">_2</b> : DecimalDigitType { }</font></div></div></div></div></div></div><div class=""><div><div><br class=""></div><div>milos</div><br class=""><blockquote type="cite" class=""><div class="">On 7 Apr 2016, at 09:44, Pyry Jahkola via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=utf-8" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Jordan,</div><div class=""><br class=""></div><div class="">Your comments brought up a few more closely related ideas that have been bubbling under.</div><div class=""><br class=""></div><div class="">To everyone,</div><div class=""><br class=""></div><div class="">Sorry for going beyond topic here. The discussion of the further proposals below should be taken into their own threads if there's interest. I'm just trying to motivate what else moving out the `<font face="Menlo" style="font-size: 11px;" class="">where</font>` clause would make possible.</div><div class=""><br class=""></div><div class=""><font size="4" class=""><b class="">1. My counter-proposal against making generic parameters public</b></font></div><br class=""><div class=""><blockquote type="cite" class=""><div class=""><div style="font-family: Helvetica; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">Another factor here is that we've been planning for a while for generic parameters to types to be exposed as implicit member typealiases, since they already conflict with the namespace for member typealiases. Therefore it's important to name generic parameters to types well, but less important to do so for generic parameters for functions. (They're also much less likely to be ad hoc for types; there has to be<span class="Apple-converted-space"> </span><i class="">something</i> that describes the relation between the Self type and the parameter, while the function might not have anything more interesting than "operand".)</div><div style="font-family: Helvetica; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""></div></div></blockquote><div class=""><br class=""></div><div class="">I disagree with that. I think it's more natural to restrict generic type parameters to the immediate local scope of the <font face="Menlo" class=""><span style="font-size: 11px;" class="">class</span></font>/<span style="font-family: Menlo; font-size: 11px;" class="">struct</span>/<span style="font-family: Menlo; font-size: 11px;" class="">enum</span> definition or extension, and simply allow making the type public with `<font face="Menlo" style="font-size: 11px;" class="">typealias</font>`. For example, this would make `<font face="Menlo" style="font-size: 11px;" class="">Element</font>` a public member of `<font face="Menlo" style="font-size: 11px;" class="">Array</font>`:</div><div class=""><br class=""></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> <b class="">public enum Result<T, Error></b> {</font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> public <b class="">typealias Value = T </b></font><span style="color: rgb(79, 122, 40); font-family: Menlo; font-size: 11px;" class="">//</span><span style="color: rgb(79, 122, 40); font-family: Menlo; font-size: 11px;" class=""> This makes `Value` public for extensions and everyone</span></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> }</font></div><div class=""><br class=""></div><div class="">I would even allow <i class="">publishing</i> the otherwise local name by repeating it in `<font face="Menlo" style="font-size: 11px;" class="">typealias</font>` like this:</div><div class=""><br class=""></div><div class=""><div class=""><font face="Menlo" style="font-size: 11px;" class=""> public struct Array<Element> { </font><span style="color: rgb(79, 122, 40); font-family: Menlo; font-size: 11px;" class="">//</span><span style="color: rgb(79, 122, 40); font-family: Menlo; font-size: 11px;" class=""> This `Element` is only available in (the missing) where clause and the scope below.</span></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> public <b class="">typealias Element = Element</b> <font color="#4f7a28" class="">// This line makes `Element` available everywhere, see below.</font></font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> }</font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""><br class=""></font></div><div class=""><span style="font-size: 11px; font-family: Menlo;" class=""> extension </span><b style="font-size: 11px; font-family: Menlo;" class="">Array<T></b><span style="font-size: 11px; font-family: Menlo;" class=""> { </span><font color="#4f7a28" style="font-size: 11px; font-family: Menlo;" class="">// <- Regardless of the pattern (`T`) used here,</font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> var mid: <b class="">Element?</b> { <font color="#4f7a28" class="">// the type `Element = T` is available here</font></font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> return ... </font><span style="color: rgb(79, 122, 40); font-family: Menlo; font-size: 11px;" class="">// because it was made public elsewhere.</span></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> }</font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> }</font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> </font><span style="font-size: 11px; font-family: Menlo;" class="">extension </span><b style="font-size: 11px; font-family: Menlo;" class="">Array<Optional<T>></b><span style="font-size: 11px; font-family: Menlo;" class=""> { <font color="#4f7a28" class="">// <- An example of pattern matching (see further below).</font></span></div><div class=""><span style="font-family: Menlo; font-size: 11px;" class=""> </span><span style="color: rgb(79, 122, 40); font-family: Menlo; font-size: 11px;" class="">// </span><span style="color: rgb(79, 122, 40); font-family: Menlo; font-size: 11px;" class="">Ditto, `Element = T?`</span></div><div class=""><span style="font-family: Menlo; font-size: 11px;" class=""><font color="#4f7a28" class=""> </font>}</span></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""><br class=""></font></div><div class=""><font style="font-size: 12px;" class=""><div style="font-size: 13px;" class=""><font face="Menlo" style="font-size: 11px;" class=""> typealias Ints = [Int]</font></div><div style="font-size: 13px;" class=""><font face="Menlo" style="font-size: 11px;" class=""> let x: Ints<b class="">.Element</b> = ... <font color="#4f7a28" class="">// Int</font></font></div><div style="font-size: 13px;" class=""><font face="Menlo" style="font-size: 11px;" class=""><br class=""></font></div></font></div><div class=""><font class="">Next, I propose how to extend this syntax with pattern matching. The above thinking is a natural progression from the use of pattern matching for introducing generic type parameters in type `<font face="Menlo" style="font-size: 11px;" class="">extension</font>`s.</font></div><div class=""><font class=""><br class=""></font></div><div class=""><font class=""><br class=""></font></div><div class=""><font size="4" class=""><b class="">2. Proposal to enable pattern matching of generic types in generic parameters</b></font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""><br class=""></font></div></div><blockquote type="cite" class=""><div class=""><div style="font-family: Helvetica; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">This is also a minor point<span class="Apple-converted-space"> </span><i class="">against</i> declaring generic parameters for extensions, since they would have to match up. We also do need a syntax some day to represent<span class="Apple-converted-space"> </span><i class="">new</i> parameters:</div><div style="font-family: Helvetica; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><blockquote class="" style="font-family: Helvetica; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px 0px 0px 40px; border: none; padding: 0px;"><div class="">// For expository purposes only:</div></blockquote><blockquote class="" style="font-family: Helvetica; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px 0px 0px 40px; border: none; padding: 0px;"><div class="">extension <T> Array where Element == Optional<T></div></blockquote><div style="font-family: Helvetica; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class=""><br class=""></div><div style="font-family: Helvetica; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px;" class="">But that deserves its own proposal. I just don't want us to paint ourselves into a corner.</div></div></blockquote><br class=""></div><div class="">I agree that we need that feature. But instead of your proposed syntax, I'd take influence from the already existing pattern matching that we have at value level, such that:</div><div class=""><br class=""></div><div class="">1. <b class="">any <i class="">generic</i> type expressions</b> within the angle brackets `<span style="font-family: Menlo; font-size: 11px;" class=""><...></span>` are taken <b class="">as patterns to match against </b> (e.g. `<span style="font-family: Menlo; font-size: 11px;" class="">Array<</span><span style="font-family: Menlo; font-size: 11px;" class="">Element</span><span style="font-family: Menlo; font-size: 11px;" class="">></span>`, `<span style="font-family: Menlo; font-size: 11px;" class="">Optional<Foo></span>`, `<span style="font-family: Menlo; font-size: 11px;" class="">Dictionary<S, S></span>`), and</div><div class="">2. <span style="font-weight: bold;" class="">all non-generic type identifiers</span><b class=""> </b>in those expressions are taken <b class="">as generic parameters</b> and not concrete types (`<span style="font-family: Menlo; font-size: 11px;" class="">Element</span>`, `<span style="font-family: Menlo; font-size: 11px;" class="">Foo</span>`, or `<span style="font-size: 11px;" class=""><font face="Menlo" class="">S</font></span>`, respectively).</div><div class=""><br class=""></div><div class="">Your example would translate into the first of these two:</div><div class=""><br class=""></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> extension <b class="">Array<Optional<T>></b> { <font color="#4f7a28" class="">// extending [T?] doesn't even need any `where` clause</font></span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> func unwrapAll() -> [T] { ... }</span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> }</span></font></div><div class=""><br class=""></div><div class=""><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> extension <b class="">Dictionary<K, Dictionary<K, V>></b> { <font color="#4f7a28" class="">// This pattern match requires the same `K` twice.</font></span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> subscript(x: K, y: K) -> V { ... }</span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> }</span></font></div><div class=""><br class=""></div><div class="">The generic parameters would shadow any existing names in the outer scope, i.e. `<font face="Menlo" style="font-size: 11px;" class="">extension Array<String></font>` would mean the same as `<font face="Menlo" style="font-size: 11px;" class="">extension Array<Element></font>`. But it would be a good idea to add a warning (or linter error) at least when stdlib types such as `<font face="Menlo" style="font-size: 11px;" class="">Swift.String</font>` are shadowed like that. I think the benefits from pattern matching outweigh the possible confusion, especially since you can't use any members of `<font face="Menlo" style="font-size: 11px;" class="">String</font>` if you mistakenly wrote `<font face="Menlo" style="font-size: 11px;" class="">extension Array<String> { ... }</font>` instead of `<font face="Menlo" style="font-size: 11px;" class="">extension Array<T> where T == String</font>`.</div><div class=""><br class=""></div></div><div class=""><div class="">With this syntax, we could also allow extending <span style="font-family: Menlo; font-size: 11px;" class="">Array</span>, <span style="font-family: Menlo; font-size: 11px;" class="">Dictionary</span>, and <span style="font-family: Menlo; font-size: 11px;" class="">Optional</span> in their more natural notation:</div><div class=""><br class=""></div></div><div class=""><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> extension <b class="">[T?]</b> {</span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> func unwrapAll() -> [T] { <font color="#919191" class="">/* ... */</font> }</span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> }</span></font></div><div class=""><div class=""><br class=""></div><div class=""><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> extension <b class="">[K: [K: V]]</b> {</span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> subscript(x: K, y: K) -> V { </span></font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" class=""><span style="font-size: 11px;" class=""> }</span></font></div><div class=""><span style="font-size: 11px; font-family: Menlo;" class=""> }</span></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""><br class=""></span></font></div></div><div class="">Here are a few more (somewhat realistically needed) examples with further `<font face="Menlo" style="font-size: 11px;" class="">where</font>` clauses:</div><div class=""><br class=""></div><div class=""><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> extension <b class="">[T] where T : Hashable</b> { </span></font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" class=""><span style="font-size: 11px;" class=""> </span></font><span style="font-family: Menlo; font-size: 11px;" class="">}</span></div><div class=""></div></div><div class=""></div></div></div><div class=""><div class=""><div class=""><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> extension <b class="">T? where T : Comparable</b> { </span></font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" class=""><span style="font-size: 11px;" class=""> </span></font><span style="font-family: Menlo; font-size: 11px;" class="">}</span></div><div class=""></div></div><div class=""></div></div></div><div class=""><div class=""><div class=""><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> extension <b class="">[K: V] where V : Equatable</b> { </span></font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" class=""><span style="font-size: 11px;" class=""> </span></font><span style="font-family: Menlo; font-size: 11px;" class="">}</span></div></div></div></div><div class=""><div class=""><div class=""><div class=""><div class=""></div></div><div class=""></div></div></div></div><div class=""><div class=""><div class=""><div class=""><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> extension <b class="">[T] where T == String</b> { </span></font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" class=""><span style="font-size: 11px;" class=""> </span></font><span style="font-family: Menlo; font-size: 11px;" class="">}</span></div><div class=""></div></div><div class=""></div></div></div><div class=""><div class=""><div class=""><div class=""></div></div></div></div></div><div class=""><br class=""></div><div class=""><div class="">I think pattern matching is a very expressive, intuitive, and readable technique that works quite well for this purpose, better than what we currently have.</div><div class=""><br class=""></div><div class=""><br class=""></div></div><div class=""><b class=""><font size="4" class="">3. Future directions</font></b></div><div class=""><br class=""></div><div class="">Brent already pointed out that the `<font face="Menlo" style="font-size: 11px;" class="">where</font>` constraint syntax could be used for dependent types (i.e. type-level values as generic parameters). Four more possible directions come to my mind:</div><div class=""><br class=""></div><div class="">(1) Adding conditional protocol conformances:</div><div class=""><br class=""></div><div class=""><div class=""><font face="Menlo" style="font-size: 11px;" class=""> extension [<b class="">T</b>]<b class="">: Equatable</b> where <b class="">T</b> : Equatable { </font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" style="font-size: 11px;" class=""> }</font></div><div class=""><div class=""><font face="Menlo" style="font-size: 11px;" class=""> extension [<b class="">T</b>]<b class="">: Comparable</b> where <b class="">T</b> : </font><span style="font-family: Menlo; font-size: 11px;" class="">Comparable</span><font face="Menlo" style="font-size: 11px;" class=""> { </font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" style="font-size: 11px;" class=""> }</font></div><div class=""></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> extension [<b class="">K</b>, <b class="">V</b>]<b class="">: Equatable</b> where <b class="">V</b> : Equatable { </font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" style="font-size: 11px;" class=""> }</font></div></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> extension Foo<<b class="">X</b>, Bar<<b class="">Y</b>>> <b class="">: Bazzable</b> where <b class="">X</b> : Baz, <b class="">Y</b> : Baz</font><font face="Menlo" style="font-size: 11px;" class=""> { </font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" style="font-size: 11px;" class=""> }</font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""><br class=""></font></div></div><div class="">(2) Extending non-nominal types:</div><div class=""><br class=""></div><div class=""><div class=""><font face="Menlo" style="font-size: 11px;" class=""> extension <b class="">(A, B)</b> { var tail: B { </font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" style="font-size: 11px;" class=""> }}</font></div><div class=""><div class=""><font face="Menlo" style="font-size: 11px;" class=""> extension <b class="">(A, B, C)</b> { var tail: (B, C) { </font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" style="font-size: 11px;" class=""> }}</font></div></div><div class=""><br class=""></div></div><div class="">(3) Using variadic patterns (shamefully borrowing the `<font face="Menlo" style="font-size: 11px;" class="">...</font>` notation from C++ here to mean an arbitrary-length list of patterns to match or expressions to expand):</div><div class=""><br class=""></div><div class=""><div class=""><font face="Menlo" style="font-size: 11px;" class=""> extension <b class="">(T...) : Equatable where T : Equatable...</b> {</font><font face="Menlo" style="font-size: 11px;" class="">}</font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""><br class=""></font></div><div class=""><font face="Menlo" style="font-size: 11px;" class=""> func == <b class=""><T...></b>(lhs: <b class="">(T...)</b>, rhs: <b class="">(T...)</b>) -> Bool <b class="">where T : Equatable...</b> {</font><font face="Menlo" style="font-size: 11px;" class=""> </font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/* ... */</span><font face="Menlo" style="font-size: 11px;" class=""> </font><font face="Menlo" style="font-size: 11px;" class="">}</font></div><div class=""><br class=""></div><div class="">(4) Since all type constraints with `<font face="Menlo" style="font-size: 11px;" class="">:</font>` fly out to of the generic parameter list into the `<font face="Menlo" style="font-size: 11px;" class="">where</font>` clause, we could enable the use of colons to give labels to generic parameters (and thus even make some of them have default values):</div><div class=""><br class=""></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> struct Parser<<b class="">encoding:</b> Encoding, <b class="">input:</b> Input></span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> where Encoding : EncodingProtocol </span></font><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">/*, ... */</span></div><div class=""><span style="font-size: 11px; font-family: Menlo;" class=""> {</span></div><div class=""><span style="font-family: Menlo; font-size: 11px;" class=""> </span><span style="color: rgb(145, 145, 145); font-family: Menlo; font-size: 11px;" class="">// ...</span></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""><font color="#919191" class=""> </font>}</span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""><br class=""></span></font></div><div class=""><font face="Menlo" class=""><span style="font-size: 11px;" class=""> let parser = Parser<<b class="">encoding:</b> UTF8, <b class="">input:</b> String>()</span></font></div><div class=""><br class=""></div><div class="">— Pyry</div><div class=""><br class=""></div></div></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class="">https://lists.swift.org/mailman/listinfo/swift-evolution<br class=""></div></blockquote></div><br class=""></div></body></html>