I like Greg Parkers suggestion, if the extension is of a type that is not part of the project/library that is being developed then you don't need override. This would allow after-the-fact extensions to library and third-party structure/classes. It is also not confusing to human or compiler, since this is not source code you are looking at (by definition).<br><br>On Thursday, 7 January 2016, Matthew Johnson via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><br><div><blockquote type="cite"><div>On Jan 6, 2016, at 3:48 AM, Greg Parker via swift-evolution <<a href="javascript:_e(%7B%7D,'cvml','swift-evolution@swift.org');" target="_blank">swift-evolution@swift.org</a>> wrote:</div><br><div><blockquote type="cite" style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br>On Jan 5, 2016, at 8:50 PM, Brent Royal-Gordon via swift-evolution <<a href="javascript:_e(%7B%7D,'cvml','swift-evolution@swift.org');" target="_blank">swift-evolution@swift.org</a>> wrote:<br><br><blockquote type="cite">Taking inspiration from syntax used for methods in classes that override methods in superclasses, require methods that override dynamically dispatched default implementations in protocol extensions to use the override keyword. Likewise, forbid the override keyword if the method being implemented instead 'masks' (would that be the right word?) a statically dispatched method in a protocol extension which can nonetheless be invoked by upcasting to the protocol.<br></blockquote><br>This has been suggested before, usually in the form of a separate `implement` keyword. The main problem is that it makes it impossible to write a protocol after the fact which formalizes some existing pattern in the types.<br><br>What do I mean by that? Well, imagine you need generic access to the `min` and `max` static properties of the various integer types. There's no existing protocol that includes those members. But you can write one and then extend the integer types to conform to your new protocol:<br><br><span style="white-space:pre-wrap"> </span>protocol BoundedIntegerType: IntegerType {<br><span style="white-space:pre-wrap"> </span><span style="white-space:pre-wrap"> </span>static var min: Self { get }<br><span style="white-space:pre-wrap"> </span><span style="white-space:pre-wrap"> </span>static var max: Self { get }<br><span style="white-space:pre-wrap"> </span>}<br><span style="white-space:pre-wrap"> </span>extension Int: BoundedType {}<br><span style="white-space:pre-wrap"> </span>extension Int8: BoundedType {}<br><span style="white-space:pre-wrap"> </span>extension Int16: BoundedType {}<br><span style="white-space:pre-wrap"> </span>extension Int32: BoundedType {}<br><span style="white-space:pre-wrap"> </span>extension Int64: BoundedType {}<br><br><span style="white-space:pre-wrap"> </span>func printLowestPossibleValueOfValue<Integer: BoundedIntegerType>(x: Integer) {<br><span style="white-space:pre-wrap"> </span><span style="white-space:pre-wrap"> </span>print(Integer.min)<br><span style="white-space:pre-wrap"> </span>}<br><br>This only works because `min` and `max` *don't* need any special marking to be used to satisfy a requirement. Requiring a keyword like you suggest would remove that feature.<br></blockquote><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important">Possible solution: if you want a new protocol adoption to map to some existing method or property then you must explicitly write that. You can't just adopt the protocol in an empty extension.</span><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important"> extension Int: BoundedType {</span><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important"> static var min = Int.min</span><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important"> static var max = Int.max</span><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important"> }</span><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important">but with some other syntax that isn't ambiguous. Code completion and compiler fix-its could suggest this when the class already implements something suitable.</span><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"></div></blockquote><div><br></div><div>Another option might be to allow imported definitions to be used by a conformance without the `override` marking to support retroactive modeling while requiring definitions in the same module as the conformance to explicitly specify the `override`.</div><br><blockquote type="cite"><div><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important">--<span> </span></span><br style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px"><span style="font-family:Helvetica;font-size:12px;font-style:normal;font-variant:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px;float:none;display:inline!important">Greg Parker </span><a 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</blockquote><br><br>-- <br> -- Howard.<br><br>