<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div><br></div><div><br>On Jun 16, 2016, at 5:36 PM, Paul Cantrell via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=utf-8"><blockquote type="cite" class="">On Jun 16, 2016, at 8:29 AM, Thorsten Seitz via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""></blockquote><div><blockquote type="cite" class=""><br class="Apple-interchange-newline"><div class=""><div style="font-family: HelveticaNeue; 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 class=""><div class="">Protocols are a mechanism for deriving types from each other whereas generics are a way to parameterize types. My point was that Swift's other way to parameterize types, namely by associated types, is very similar to generics with wildcards when looking a the existentials of such protocols.</div></div></div></div></blockquote><br class=""></div><div>This has been a point of confusion for me as well. I keep hearing that associated types are different from generic protocols, but this seems like a distinction without a difference.</div><div><br class=""></div><div>Suppose Swift allowed generic protocols. How would a hypothetical Collection<Foo> be different in practice from the proposed existential Any<Collection where .Element == Foo>?</div><div><br class=""></div><div>Yes, in the realm of type theory and compiler internals they might represented differently, sure. But in practice, in terms of what code can actually do? I know of only two differences:</div><div><br class=""></div><div>1. A type can only conform to any given protocol with one set of type parameters. (Nothing can be both Collection<Foo> and Collection<Bar>.)</div><div><br class=""></div><div>2. When a type conforms to Collection, it declares “associatedtype Foo” instead of “: Collection<Foo>”, and Foo can be inferred by the compiler in some circumstances. That’s handy, but it’s a syntactic difference.</div></div></blockquote><div><br></div><div>Wasn't there something recently from chris about removing inference?</div><br><blockquote type="cite"><div><div><br class=""></div><div>Is there a deeper difference I’m missing?</div><div><br class=""></div><div>Cheers, P</div><div><br class=""></div></div></blockquote><blockquote type="cite"><div><span>_______________________________________________</span><br><span>swift-evolution mailing list</span><br><span><a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a></span><br><span><a href="https://lists.swift.org/mailman/listinfo/swift-evolution">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br></div></blockquote></body></html>