<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="">Hey there,</div><div class=""><br class=""></div><div class="">I filed this bug. Sorry that I mentioned it was to do with the TODO - I tried to trace it back myself, found that the substitution map was giving a null for the same-type requirement (and that “getDependentTypes()” explicitly skips them), and assumed that was the reason. Try as I might, I couldn’t figure out how to resolve it so I assumed I was lacking requisite knowledge of substitution maps to fix it (which turns out to be correct - thanks for the great explanation, Slava!)</div><div class=""><br class=""></div><br class=""><div><blockquote type="cite" class=""><div class="">On 31 Dec 2016, at 01:09, Slava Pestov via swift-dev <<a href="mailto:swift-dev@swift.org" class="">swift-dev@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div style="font-family: Helvetica; font-size: 12px; 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="">extension Array where Element == S, Element : P {</div><div style="font-family: Helvetica; font-size: 12px; 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=""> func doSomething() {}</div><div style="font-family: Helvetica; font-size: 12px; 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><div style="font-family: Helvetica; font-size: 12px; 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=""><br class=""></div><div style="font-family: Helvetica; font-size: 12px; 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="">The ‘Element : P’ requirement is redundant and is dropped from the signature, and ‘doSomething’ has the same exact type as if we had written:</div><br class="Apple-interchange-newline"></div></blockquote><blockquote type="cite" class=""><div class="">extension Array where Element == S {</div><div class=""> func doSomething() {}</div><div class="">}</div></blockquote></div><br class=""><div class="">What if the S: P conformance is conditional or introduced by another module? The presence same-type constraint isn’t enough to say that S will _never_ conform to P (if it doesn’t already conform).</div><div class=""><br class=""></div><div class=""><br class=""></div><blockquote style="margin: 0 0 0 40px; border: none; padding: 0px;" class=""><div class=""><font face="Courier" class="">extension S: P where S.SomeType == Int, S.AnotherType: Collection, S.AnotherType.Index == SomeType {</font></div><div class=""><font face="Courier" class=""> // conform to P</font></div><div class=""><font face="Courier" class="">}</font></div><div class=""><font face="Courier" class=""><br class=""></font></div><div class=""><font face="Courier" class="">extension Array where Element == S, S.SomeType == Int, S.AnotherType: Collection, // …etc</font></div><div class=""><font face="Courier" class=""><br class=""></font></div><div class=""><font face="Courier" class="">vs</font></div><div class=""><font face="Courier" class=""><br class=""></font></div><div class=""><font face="Courier" class="">extension Array where Element == S, S: P</font></div><div class=""><br class=""></div></blockquote>- Karl</body></html>