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.error { color:#AA0000; }</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="bloop_markdown"><p>This is a different problem that protocols have today. There was some talk about having some sort of keyword like <code>implements</code> to disambiguate which from where the implementation comes from.</p>
<p>Just pretend for a second, we wouldn’t have generic protocols and implement it the SE–01242 way:</p>
<pre><code class="swift">protocol Foo {
associatedtype T
func foo()
func bar(o: T)
}
protocol IntFoo : Foo where T == Int {}
protocol StringFoo : Foo where T == String {}
// Where do you want your extension?
extension Foo {
func foo() {
// cannot call bar from here, we don't know what T is
}
}
extension Foo where T == String {
func foo() {
self.bar(o: "works fine") // calls a function that accepts a String
}
}
extension Foo where T == Int {
func foo() {
self.bar(o: 42) // calls a function that accepts an Int
}
}
class MyClass : IntFoo, StringFoo {
// implement bar for Int and String
// foo is problematic here already, and we haven't talked about generic protocols yet
}
</code></pre>
<p>See it’s not the problem of the generic protocols but the overlapping function <code>foo</code> of different protocols <code>IntFoo</code> and <code>StringFoo</code>.</p>
<p>In general <code>Foo<T></code> would have the same problem. It should be solved in a different way, which is not part of this pitch.</p>
<p></p></div><div class="bloop_original_html"><style>body{font-family:Helvetica,Arial;font-size:13px}</style><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div> <br> <div id="bloop_sign_1480774192011265024" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">-- <br>Adrian Zubarev<br>Sent with Airmail</div></div> <br><p class="airmail_on">Am 3. Dezember 2016 um 15:07:03, Daniel Leping (<a href="mailto:daniel@crossroadlabs.xyz">daniel@crossroadlabs.xyz</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>
<title></title>
<div style="white-space:pre-wrap">Ok. Let's say I have a generic
protocol P<T> with two methods:<br>
func foo()<br>
func bar(o:T)<br>
<br>
I have a default implementation of foo, which internally calls
bar.<br>
<br>
How would work foo once a class implements P<Int> and
P<String>?</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Sat, 3 Dec 2016 at 15:26 Adrian Zubarev 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 class="m_-3691223278462264745bloop_markdown gmail_msg">
<p class="gmail_msg">I believe generic protocols could be used as a
shortcut for protocols with associated types.</p>
<pre class="gmail_msg"><code class="m_-3691223278462264745swift gmail_msg">// Protocol with associated type
protocol Foo {
associatedtype F
func foo(_ f: F)
}
// Existential
typealias IntFoo = Any<Foo> where F == Int
struct Test : IntFoo {} // error
struct Test : Foo { func foo(_: Int) {…} }
let intFoo: IntFoo = Test() // fine
// SE-0142
protocol IntFooProtocol : Foo where F == Int {}
// Generic protocols
// Autogenerated with all associated types present in the parameter list
protocol GenericFoo<F> : Foo { … }
</code></pre>
<p class="gmail_msg">Instead of creating new protocol for a
different subset of types constrained by the where clause, this
approach could come really handy.</p>
<p class="gmail_msg">Does it affect stdlib and/or ABI somehow? When
SE–0142 is implemented to improve the stdlib, wouldn’t that mean
that more types like <code class="gmail_msg">IntFooProtocol</code>
from above will spawn?</p>
<p class="gmail_msg"></p>
</div>
<div class="m_-3691223278462264745bloop_original_html gmail_msg">
</div>
</div>
<div style="word-wrap:break-word" class="gmail_msg">
<div class="m_-3691223278462264745bloop_original_html gmail_msg">
<div id="m_-3691223278462264745bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto" class="gmail_msg"><br class="gmail_msg"></div>
<br class="gmail_msg">
<div id="m_-3691223278462264745bloop_sign_1480770382034871040" class="m_-3691223278462264745bloop_sign gmail_msg">
<div style="font-family:helvetica,arial;font-size:13px" class="gmail_msg">-- <br class="gmail_msg">
Adrian Zubarev<br class="gmail_msg">
Sent with Airmail</div>
</div>
<br class="gmail_msg"></div>
</div>
<div style="word-wrap:break-word" class="gmail_msg">
<div class="m_-3691223278462264745bloop_original_html gmail_msg">
<p class="m_-3691223278462264745airmail_on gmail_msg">Am 3.
Dezember 2016 um 13:47:13, Anders Ha (<a href="mailto:hello@andersio.co" class="gmail_msg" target="_blank">hello@andersio.co</a>) schrieb:</p>
<blockquote type="cite" class="m_-3691223278462264745clean_bq gmail_msg">
<div dir="auto" class="gmail_msg">
<div class="gmail_msg"></div>
<div class="gmail_msg">
<div class="gmail_msg"><span class="gmail_msg">This is called
generalized existentials. It is included in the Generic Manifesto,
has been discussed quite a few times with long email chains before,
and spawned the change to the `protocol<>` syntax as kinda a
precursor. It would be surprised if Swift 4 Phase 2 doesn't have it
given its popularity.</span></div>
<div class="gmail_msg"><span class="gmail_msg"><br class="gmail_msg"></span></div>
<div class="gmail_msg"><span class="gmail_msg">Regards</span></div>
<div class="gmail_msg"><span class="gmail_msg">Anders</span></div>
<div class="gmail_msg"><span class="gmail_msg"><br class="gmail_msg">
On 2 Dec 2016, at 20:13, Charles Srstka via swift-evolution
<<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:<br class="gmail_msg">
<br class="gmail_msg"></span></div>
<blockquote type="cite" class="gmail_msg">
<div class="gmail_msg">
<blockquote type="cite" class="gmail_msg"><span class="gmail_msg">On Dec 2, 2016, at 12:34 PM, Adrian Zubarev via
swift-evolution <<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>>
wrote:<br class="gmail_msg"></span></blockquote>
<div class="gmail_msg">
<blockquote type="cite" class="gmail_msg"><span class="gmail_msg"><br class="m_-3691223278462264745Apple-interchange-newline gmail_msg"></span>
<div class="gmail_msg">
<p style="margin:15px 0px;font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="gmail_msg"><span class="gmail_msg">I just overlooked that
the subsection about generic protocols was inside the<span class="m_-3691223278462264745Apple-converted-space gmail_msg"> </span><strong class="gmail_msg">Unlikely</strong><span class="m_-3691223278462264745Apple-converted-space gmail_msg"> </span>section.</span></p>
<p style="margin:15px 0px;font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="gmail_msg">The problem is that I need a way to refer to a
function with a specific name. Plus the connection type has to have
a specific API, like having a DispatchQueue and know the router
object if there is any (sounds like a protocol right?!). The
function reference should also keep the connection object alive
with a strong reference.<span class="m_-3691223278462264745Apple-converted-space gmail_msg"> </span></p>
<p style="margin:15px 0px;font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="gmail_msg"><code style="font-family:Menlo,Consolas,'Liberation Mono',Courier,monospace;font-size:10pt;border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;background-color:rgb(248,248,248);color:inherit;border:1px solid rgb(234,234,234);margin:0px 2px;padding:0px 5px;word-break:normal;word-wrap:normal" class="gmail_msg">associatedtype</code><span class="m_-3691223278462264745Apple-converted-space gmail_msg"> </span>does
not solve that problem for me.</p>
<p style="margin:15px 0px;font-family:Helvetica,Arial;font-size:13px;font-style:normal;font-variant-caps:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px" class="gmail_msg">I clearly see that generic protocols overlap
with<span class="m_-3691223278462264745Apple-converted-space gmail_msg"> </span><code style="font-family:Menlo,Consolas,'Liberation Mono',Courier,monospace;font-size:10pt;border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;background-color:rgb(248,248,248);color:inherit;border:1px solid rgb(234,234,234);margin:0px 2px;padding:0px 5px;word-break:normal;word-wrap:normal" class="gmail_msg">associatedtype</code><span class="m_-3691223278462264745Apple-converted-space gmail_msg"> </span>but
couldn’t we find a compromise here? For instance like Chris Lattner
introduced generic type aliases without the ability of
constants.</p>
</div>
</blockquote>
</div>
<div class="gmail_msg">Why don’t we just use angle brackets to
specify associated types? Protocols aren’t using them for anything
anyway. Then you could:</div>
<div class="gmail_msg"><br class="gmail_msg"></div>
<div class="gmail_msg">if let someSequence as?
Sequence<Iterator.Element == Int> { // do something }</div>
<div class="gmail_msg"><br class="gmail_msg"></div>
<div class="gmail_msg">which would form a nice parallel to the
syntax for casting things to generic types.</div>
<div class="gmail_msg"><br class="gmail_msg"></div>
<div class="gmail_msg">Charles</div>
<div class="gmail_msg"><br class="gmail_msg"></div>
</div>
</blockquote>
<blockquote type="cite" class="gmail_msg">
<div class="gmail_msg"><span class="gmail_msg">_______________________________________________</span><br class="gmail_msg">
<span class="gmail_msg">swift-evolution mailing
list</span><br class="gmail_msg">
<span class="gmail_msg"><a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a></span><br class="gmail_msg">
<span class="gmail_msg"><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="gmail_msg" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br class="gmail_msg">
</div>
</blockquote>
</div>
</div>
</blockquote>
</div>
</div>
_______________________________________________<br class="gmail_msg">
swift-evolution mailing list<br class="gmail_msg">
<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a><br class="gmail_msg">
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</blockquote>
</div>
</div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>