<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=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jun 16, 2016, at 10:50 AM, Matthew Johnson <<a href="mailto:matthew@anandabits.com" class="">matthew@anandabits.com</a>> wrote:</div><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=""><blockquote type="cite" class=""><div class=""><br class="Apple-interchange-newline">On Jun 16, 2016, at 10:36 AM, Paul Cantrell 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=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="">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 class=""><br class=""></div><div class="">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></div></blockquote><div class=""><br class=""></div><div class="">If Collection were a Java-like generic protocol you would have 5 generic parameters, all of which must be explicitly provided with arguments when forming an existential, although the arguments could be wildcards. This is a bit unwieldy.</div></div></div></blockquote><div><br class=""></div><div>Yes. This was #2 on my list. A very, very nice syntactic difference — nonrepetition of redundant type information is so much of what makes Swift great. — but only a syntactic difference.</div><div><br class=""></div><br class=""><blockquote type="cite" class=""><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=""><blockquote type="cite" class=""><div class=""><div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="">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 class=""><br class=""></div><div class="">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></div></blockquote><div class=""><br class=""></div><div class="">This is a pretty huge difference. Multiple conformances are on the unlikely list for Swift and generic protocol syntax implies multiple conformances are possible (as is the case in at least some languages).</div></div></div></blockquote></div><br class=""><div class="">Right. Is that it? Are associated types really just generic protocols + single conformance constraint + type params inferred / implied?</div><div class=""><br class=""></div><div class="">P</div></body></html>