<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 Dec 20, 2015, at 8:27 AM, Stephen Celis 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=""><blockquote type="cite" class=""><div class="">On Dec 19, 2015, at 11:14 PM, Dave Abrahams 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=""><blockquote type="cite" style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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="">On Dec 19, 2015, at 5:09 PM, Brent Royal-Gordon via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class="">I don't think `required` captures the intended meaning *at all*. You're not required to declare the type of a "required typealias"—it's often, perhaps even usually, inferred.<br class=""></blockquote><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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=""><span style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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; float: none; display: inline !important;" class="">No, but it is required to exist and can't always be inferred. It puts a constraint on the type that is declared to conform. This is a requirement in exactly the same sense that other protocol requirements are requirements. Notably operator requirements may be satisfied "implicitly" by declarations that already exist, but they are still requirements.</span><br style="font-family: Helvetica; font-size: 12px; font-style: normal; font-variant: 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></blockquote><div class=""><br class=""></div><div class="">I think reusing "required" here (where "typealias" has already been reused) could make the concept of associated types more opaque to new users.</div></div></div></div></blockquote><br class=""></div><div>I agree. There are a couple of potentially confusing issues here:</div><div><br class=""></div><div>- In principle, all of the declarations in the protocol are “requirements” that a type needs to fulfill to conform to the protocol.</div><div>- Except for optional requirements in @objc protocols.</div><div>- Except for requirements with default implementations (which currently cannot be written inline in the protocol, but should be allowed some day). Today’s typealiases can have "default implementations” as well.</div><div><br class=""></div><div>-Chris</div><div><br class=""></div><br class=""></body></html>