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.
I understand the mechanism which calls StringLiteralConvertible's
init(stringLiteral) under the hood:
let a: SomeStringLiteralConvertibleType = "hello"
I also understand the magic in the pattern matching operator. But I don't
understand why when associating them together:
func ~=(lhs: SomeStringLiteralConvertibleType, rhs: String) -> Bool {
return false
}
Then creates his behaviour in all Enums with String raw values:
enum MyEnum: String {
case Super = "super"
}
let a = MyEnum(rawValue: "super") // nil
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.
David
> On 05 Jan 2016, at 18:26, David Hart via swift-users <[email protected]>
> 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.
>
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