[swift-evolution] [swift-users] Very strange automatic behavior between StringLiteralConvertible and pattern matching
David Hart
david at hartbit.com
Tue Jan 5 11:30:11 CST 2016
Sorry about the double post.
> On 05 Jan 2016, at 18:26, David Hart via swift-users <swift-users at swift.org> wrote:
>
> How is it that Swift allows code like this:
>
> struct Sneaky: StringLiteralConvertible {
> init(stringLiteral value: String) {}
> init(extendedGraphemeClusterLiteral value: String) {}
> init(unicodeScalarLiteral value: String) {}
> }
>
> func ~=(sneaky: Sneaky, string: String) -> Bool {
> return false
> }
>
> enum NormalEnum: String {
> case Super = "super"
> case Mario = "mario"
> }
>
> let value = NormalEnum(rawValue: "super”) // return nil!!!!
>
> It hit completely by surprise today because of of a Regex library:
>
> struct Regex: StringLiteralConvertible {
> init(stringLiteral value: String) {}
> init(extendedGraphemeClusterLiteral value: String) {}
> init(unicodeScalarLiteral value: String) {}
>
> //...
> }
>
> func ~=(regex: Regex, string: String) -> Bool {
> return regex.matches(string)
> }
>
> If I was not already a Swift enthusiast, this behaviour would have left me completely dumbfounded.
> What can we do about it?
>
> David.
>
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
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