<div dir="ltr">Hi,<div><br></div><div>Could you point to what Regex code are you using? You mention you copy some library but don't provide the original source.</div></div><br><div class="gmail_quote"><div dir="ltr">On Wed, Jan 6, 2016 at 9:12 AM David Hart via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto"><div>I'm starting to understand. The implementation of RawRepresentable's probably looks like this:</div><div><br></div><div>init?(rawValue: String) {</div><div> switch rawValue {</div><div> case "firstValue": self = .FirstCase</div><div> case "secondValue": self = .SecondCase</div><div> default: return nil</div><div> }</div><div>}</div><div><br></div><div>In that case (no pun intended), the switch cases are converted to <span style="background-color:rgba(255,255,255,0)">SomeStringLiteralConvertibleType and then pattern matched.</span></div><div><span style="background-color:rgba(255,255,255,0)"><br></span></div><div><span style="background-color:rgba(255,255,255,0)">But shouldn't the implementation of switch refrain from any complicated casting when the types correspond?</span></div><div><span style="background-color:rgba(255,255,255,0)"><br></span></div><div><span style="background-color:rgba(255,255,255,0)">David.</span></div></div><div dir="auto"><div><br>On 06 Jan 2016, at 10:20, David Hart via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><div>To bring a little bit more context: I copied this Regex library in my project which had StringLiteralConvertible and implemented the pattern matching operator and all of a sudden, ALL init(rawValue: String) calls of completely unrelated enums started returning unexpected values. If I did not have unit tests, I probably would not have found out about it for a while.</div><div><br></div><div>I understand the mechanism which calls StringLiteralConvertible's init(stringLiteral) under the hood:</div><div><br></div><div>let a: SomeStringLiteralConvertibleType = "hello"</div><div><br></div><div>I also understand the magic in the pattern matching operator. But I don't understand why when associating them together:</div><div><br></div><div>func ~=(lhs: <span style="background-color:rgba(255,255,255,0)">SomeStringLiteralConvertibleType, rhs: String) -> Bool {</span></div><div><span style="background-color:rgba(255,255,255,0)"> return false</span></div><div>}</div><div><br></div><div>Then creates his behaviour in all Enums with String raw values:</div><div><br></div><div>enum MyEnum: String {</div><div> case Super = "super"</div><div>}</div><div><br></div><div>let a = MyEnum(rawValue: "super") // nil</div><div><br></div><div>I can't figure out if this is just a confusing behaviour of Swift, in which case I want to write a proposal to make it less confusing, or if it is a big with Swift, in which case I should open a bug report.</div><div><br></div><div>David</div><div><br>On 05 Jan 2016, at 18:26, David Hart via swift-users <<a href="mailto:swift-users@swift.org" target="_blank">swift-users@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><div><span style="background-color:rgba(255,255,255,0)">How is it that Swift allows code like this:</span><div><span style="background-color:rgba(255,255,255,0)"><br></span></div><div><span style="background-color:rgba(255,255,255,0)"><font>struct Sneaky: StringLiteralConvertible {<br><span style="white-space:pre-wrap"> </span>init(stringLiteral value: String) {}<br><span style="white-space:pre-wrap"> </span>init(extendedGraphemeClusterLiteral value: String) {}<br><span style="white-space:pre-wrap"> </span>init(unicodeScalarLiteral value: String) {}<br>}<br><br>func ~=(sneaky: Sneaky, string: String) -> Bool {<br><span style="white-space:pre-wrap"> </span>return false<br>}<br><br>enum NormalEnum: String {<br><span style="white-space:pre-wrap"> </span>case Super = "super"<br><span style="white-space:pre-wrap"> </span>case Mario = "mario"<br>}</font><br><br><font>let value = NormalEnum(rawValue: "super”) // return nil!!!!</font></span></div><div><span style="background-color:rgba(255,255,255,0)"><br></span></div><div><span style="background-color:rgba(255,255,255,0)">It hit completely by surprise today because of of a Regex library:</span></div><div><span style="background-color:rgba(255,255,255,0)"><br></span></div><div><font style="background-color:rgba(255,255,255,0)">struct Regex: StringLiteralConvertible {<br><span style="white-space:pre-wrap"> </span>init(stringLiteral value: String) {}<br><span style="white-space:pre-wrap"> </span>init(extendedGraphemeClusterLiteral value: String) {}<br><span style="white-space:pre-wrap"> </span>init(unicodeScalarLiteral value: String) {}</font></div><div><font style="background-color:rgba(255,255,255,0)"><br></font></div><div><span style="background-color:rgba(255,255,255,0)"><font><span style="white-space:pre-wrap"> </span>//...<br>}<br><br>func ~=(regex: Regex, string: String) -> Bool {<br><span style="white-space:pre-wrap"> </span>return regex.matches(string)<br>}</font><br></span></div><div><span style="background-color:rgba(255,255,255,0)"><br></span></div><div><span style="background-color:rgba(255,255,255,0)">If I was not already a Swift enthusiast, this behaviour would have left me completely dumbfounded.</span></div><div><span style="background-color:rgba(255,255,255,0)">What can we do about it?</span></div><div><span style="background-color:rgba(255,255,255,0)"><br></span></div><div><span style="background-color:rgba(255,255,255,0)">David.</span></div></div>
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