<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div>I still think that, except in certain very generic cases, default methods are something I would be wary of being easily abused.</div><div id="AppleMailSignature"><br></div><div id="AppleMailSignature">Protocols, Java style interfaces, they allow users to focus only on a generic behaviour/contract without having to rely or being able to rely and/or make bonding assumptions on any implementation details of the type conforming to the protocol. Default methods in a protocol still seem to go in the opposite direction although they do offer a lot of convenience and open up new styles.<br><br>Sent from my iPhone</div><div><br>On 16 Jan 2016, at 11:04, Haravikk via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=utf-8"><div class="">I think that the point of allowing defaults in protocols is so that you can assume a default for all types conforming to that protocol. To use your example, if you receive an instance of Name, you can only call printSomething() without arguments if you test that it is an instance of type Name. If instead you test its conformance to the Good protocol (which you might do if there are a lot of different types conforming to Good) then you have to provide a value, because you can’t infer that every possible implementation will have a default.</div><div class=""><br class=""></div><div class="">Regarding this proposal however I think it might be useful to have a distinction between a protocol function that specifies a default value for all implementations (that they must all conform to) versus one that specifies that implementations must have a default value, but not what that value must be.</div><div class=""><br class=""></div><div class="">For example, to have a fixed and altered default we currently we have to do things like this:</div><div class=""><br class=""></div><div class=""><div class="">protocol Protocol {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>func functionWithSpecificDefault(argument:String)</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>func functionWithAnyDefault(argument:String)</div><div class="">}</div></div><div class=""><br class=""></div><div class="">extension Protocol {</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func functionWithSpecificDefault() { self.functionWithSpecificDefault(“Foo”) }</div><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func functionWithAnyDefault() { self.functionWithAnyDefault(“Foo”) }</div><div class="">}</div><div class=""><br class=""></div><div class="">class MyClass : Protocol {</div><span class="Apple-tab-span" style="white-space: pre;"> </span>func functionWithSpecificDefault(argument:String) { /* Implementation here */ }<div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func functionWithAnyDefault(argument:String) { /* Implementation here */ }</div><div class=""><br class=""><div class=""><span class="Apple-tab-span" style="white-space:pre"> </span>func functionWithAnyDefault() { self.functionWithAnyDefault(“Bar”) } // Override default</div><div class="">}</div><div class=""><br class=""></div><div class="">Which could be replaced by:</div><div class=""><br class=""></div><div class="">protocol Protocol {</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>func functionWithSpecificDefault(argument:String = “Foo")</div><div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>func functionWithAnyDefault(argument:String = default)</div><div class="">}</div><div class=""><br class=""></div><div class="">class MyClass : Protocol {</div><span class="Apple-tab-span" style="white-space: pre;"> </span>func functionWithSpecificDefault(argument:String = “Foo") { /* Implementation here */ }<div class=""><span class="Apple-tab-span" style="white-space: pre;"> </span>func functionWithAnyDefault(argument:String = “Bar") { /* Implementation here */ }</div><div class="">}</div><div class=""><br class=""></div><div class="">However, this has the added advantage that implementing functionWithSpecificDefault with a default other than “Foo” would cause a compiler error, while doing so for functionWithAnyDefault would not (but specifying no default at all would, as one is required).</div><br class=""><div><blockquote type="cite" class=""><div class="">On 16 Jan 2016, at 10:15, 肇鑫 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 dir="ltr" class=""><div class="gmail_default" style="font-family:georgia,serif">No. Although you protocol's function doesn't has a default parameter value. Your implementation does. So you don't need to define another func function() in your protocol.</div><div class="gmail_default" style="font-family:georgia,serif"><br class=""></div><div class="gmail_default"><div class="gmail_default"><font face="georgia, serif" class="">protocol Good {</font></div><div class="gmail_default"><font face="georgia, serif" class=""> func printSomething(something:String)</font></div><div class="gmail_default"><font face="georgia, serif" class="">}</font></div><div class="gmail_default"><font face="georgia, serif" class=""><br class=""></font></div><div class="gmail_default"><font face="georgia, serif" class="">struct Name:Good {</font></div><div class="gmail_default"><font face="georgia, serif" class=""> func printSomething(something: String = "John") {</font></div><div class="gmail_default"><font face="georgia, serif" class=""> print(something)</font></div><div class="gmail_default"><font face="georgia, serif" class=""> }</font></div><div class="gmail_default"><font face="georgia, serif" class="">}</font></div><div class="gmail_default"><font face="georgia, serif" class=""><br class=""></font></div><div class="gmail_default"><font face="georgia, serif" class="">Name().printSomething()</font></div><div class="gmail_default"><font face="georgia, serif" class=""><br class=""></font></div><div class="gmail_default"><font face="georgia, serif" class="">above code works.</font></div><div class="gmail_default"><font face="georgia, serif" class=""><br class=""></font></div><div class="gmail_default"><font face="georgia, serif" class="">zhaoxin</font></div></div></div><div class="gmail_extra"><br class=""><div class="gmail_quote">On Sat, Jan 16, 2016 at 6:05 PM, Vatsal Manot <span dir="ltr" class=""><<a href="mailto:vatsal.manot@yahoo.com" target="_blank" class="">vatsal.manot@yahoo.com</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class=""><div class="">It serves as a better (if not simpler) substitute for the following pattern:</div><div class=""> </div><span class="">protocol Protocol<br class=""></span><span class="">{<br class=""></span><span class=""> typealias Argument<br class=""></span><span class=""> <br class=""></span><span class=""> func function()<br class=""></span><span class=""> func function(_: Argument)<br class=""></span><div class=""><div class="h5"><span class="">}<br class=""></span><span class=""> <br class=""></span><div class=""><div class=""><blockquote type="cite" class=""><div class="">On 16-Jan-2016, at 3:29 PM, 肇鑫 <<a href="mailto:owenzx@gmail.com" target="_blank" class="">owenzx@gmail.com</a>> wrote:</div><br class=""><div class=""><div dir="ltr" class=""><div class="gmail_default" style="font-family:georgia,serif">I wonder where is the good for a protocol designer on this?<br class=""></div><div class="gmail_default" style="font-family:georgia,serif"><br class=""></div><div class="gmail_default" style="font-family:georgia,serif">zhaoxin</div><div class="gmail_extra"><br class=""><div class="gmail_quote">On Sat, Jan 16, 2016 at 5:23 PM, Vatsal Manot via swift-evolution <span dir="ltr" class=""><<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Currently, the following the code fails with multiple errors:<br class="">
<br class="">
protocol Protocol<br class="">
{<br class="">
typealias Argument<br class="">
<br class="">
func function(argument: Argument = default)<br class="">
}<br class="">
<br class="">
I propose that we allow protocols to require functions with default parameter values. I can’t see any disadvantages to this, and the change would only be additive.<br class="">
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</blockquote></div><br class=""><br clear="all" class=""><div class=""><br class=""></div>-- <br class=""><div class=""><div dir="ltr" class=""><div class=""><br class="">Owen Zhao<br class=""></div></div></div>
</div></div>
</div></blockquote></div><br class=""></div></div></div></div></blockquote></div><br class=""><br clear="all" class=""><div class=""><br class=""></div>-- <br class=""><div class="gmail_signature"><div dir="ltr" class=""><div class=""><br class="">Owen Zhao<br class=""></div></div></div>
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