<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=""><div class="">Dmitri, Slava and Doug thank you for taking the time to respond. I apologize for not thanking you sooner. </div><div class=""><br class=""></div><div class="">Since the core team has a loosely shared understanding of the goals but hasn't had time to write it down yet I thought it might be helpful if I put together a summary of the features that seem to me like obvious candidates for completing the current generic system. If I have missed anything significant please point that out. </div><div class=""><br class=""></div><div class="">I'm placing a "**" next to items that I beleive I have seen mentioned by the core team as desired features. This is based on memory and may be innacurate or may be based on desires expressed, but not necessarily pinned to the Swift 3 timeline. </div><div class=""><br class=""></div><div class="">I'm hoping the core team might be able to indicate which items are likely to be part of the work you're doing on Swift 3, which items you might be interested in the community contributing to, and which items are unliekly to be considered during the Swift 3 timeframe even with community involvement. This could help interested contributors start thinking about what they might be interested in working on while we wait for a more complete document describing the vision.</div><div class=""><br class=""></div><div class="">- ** generic typealias</div><div class=""><br class=""></div><div class="">- allow protocols to specify a non-covarying Self in static method declarations (a possible solution to the problem of conforming non-final classes in Cocoa to protocols containing factory methods)</div><div class=""><br class=""></div><div class="">- extensions</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** allow same type constraints</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** allow protocol conformance in constrained extensions</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- allow protocol conformance in protocol extensions</div><div class=""><br class=""></div><div class="">- associated type constraints</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- use of Self as a superclass constraint</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** where clause constraining inidividual associated types</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** where clause relating multiple assocated types</div><div class=""><br class=""></div><div class="">- existentials for protocols with associated types</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- protocol existentials don't conform to the protocol itself</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** fully bound: protocol<GeneratorType where Element == Int> </div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** fully constrained: protocol<GeneratorType where Element: CustomStringConvertible></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- partially bound / constrained - allow access to members only mentioning constrained associated types</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** unbound - allow access to members not mentioning Self or associated types</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- composition: protocol<P1, P2 where P1.Associated: P3, P2.Associated == Int, P1.Other == P2.Other></div><div class=""><br class=""></div><div class="">- nesting (per Slava's email)</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** Generic types nested inside generic functions</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** Generic types nested inside generic types</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- ** Generic functions nested inside generic functions which capture values or outer generic types</div><div class=""><br class=""></div><div class="">Some things that I expect are out of scope for Swift 3 but am mentioning for completeness / confirmation of that:</div><div class=""><br class=""></div><div class="">- variadic generics</div><div class="">- higher kinded types</div><div class="">- higher rank types</div><div class=""><br class=""></div><div class="">Thanks,</div><div class="">Matthew</div></div><div class=""><br class=""></div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On Dec 11, 2015, at 11:24 PM, Douglas Gregor <<a href="mailto:dgregor@apple.com" class="">dgregor@apple.com</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=""><br class=""><div class=""><blockquote type="cite" class=""><div class="">On Dec 10, 2015, at 3:45 PM, Matthew Johnson 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="">One of the stated focus areas for Swift 3 is to complete the generics system. <div class=""><br class=""></div><div class="">How far along is the design for the “complete” generics system? </div></div></div></blockquote><div class=""><br class=""></div><div class="">There’s a loose shared understanding of the pieces we need among the compiler and standard library developers that have been co-evolving the generics system, but it’s not written down in any single place.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Is there appetite among the core team to involve the community in evaluating planned features or submitting proposals to complement existing plans?</div></div></div></blockquote><div class=""><br class=""></div><div class="">Yes, absolutely. I feel like we (the core team) need to articulate our vision here—what we feel we need to accomplish (in features, in the standard library API, in the implementation) in Swift 3 vs. what we believe we can introduce later on, how the pieces all fit together, etc.—to help facilitate those discussions.</div><br class=""><blockquote type="cite" class=""><div class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">Also, is there any documentation other than <a href="https://github.com/apple/swift/blob/master/docs/Generics.rst" class="">https://github.com/apple/swift/blob/master/docs/Generics.rst</a> describing in detail what the complete vision for the generics system is and what new features will be added in Swift 3 (as well as any generics features that have been decided against for Swift or version 3 specifically)?</div></div></div></blockquote><br class=""></div><div class="">No, that document is the best overall documentation for the vision of the generics system, despite being mostly untouched for more than two years and lacking newer features (protocol extensions, anyone?).</div><div class=""><br class=""></div><div class="">So, we need to write up a document describing our vision here. It’s going to take a little time, both because it’s a nontrivial task and because the likely principal authors are also engaged in other large Swift 3 tasks (e.g., <a href="https://github.com/apple/swift-evolution/blob/master/proposals/0005-objective-c-name-translation.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0005-objective-c-name-translation.md</a>)</div><div class=""><br class=""></div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>- Doug</div><div class=""><br class=""></div><br class=""></div></div></blockquote></div><br class=""></body></html>