> On Oct 3, 2016, at 12:50 PM, Adrian Zubarev via swift-evolution
> <[email protected]> wrote:
>
> Hi there,
>
> I’m interested if this idea has some potential future in Swift or not.
>
> Currently RawRepresentable enums accept only a subset of literal types like
> String, Character and the Integer family (enum Name : String { … }).
>
> Sometimes this is not enough for my use-case and I wish I could feed my enums
> with other Hashable types!
>
> As a workaround I can create a custom struct or even a class and conform it
> to RawRepresentable and fake an enum with some static variables (similar to
> what is done with OptionSet types).
>
>
The literal type constraint only affects the sugar syntax using the ': String'
and 'case X = 1' syntax. If you write an enum's conformance explicitly, you can
use any raw type you like:
enum Test: RawRepresentable {
case something, nothing
init?(rawValue: A) {
switch rawValue.value {
case "something": self = .something
case "nothing": self = .nothing
default: return nil
}
}
var rawValue: A {
switch self {
case .something: return A(value: "something")
case .nothing: return A(value: "nothing")
}
}
}
though it's up to you at this point to guarantee the 1:1 correspondence between
raw values and enum values that RawRepresentable assumes.
-Joe
> The problem there is that I cannot use the same switch pattern matching like
> with enums. I’d wish either enums could accept Hashable types (maybe with
> some restriction) or the existence on a protocol to build custom enum-like
> types with strucs/classes and use the same switch pattern matching.
>
> struct A : Hashable { /* implement everything */ }
>
> // Variant 1:
> enum Test : A {
> case something = A(rawValue: A(value: "something"))
> case nothing = A(rawValue: A(value: "nothing"))
> }
>
> // Variant 2:
>
> protocol SomeFancyName : RawRepresentable { … }
>
> struct Test : SomeFancyName {
>
> let rawValue: A
> init?(rawValue: A) {
> // Implement + reject unwanted `A`s
> }
>
> static let something = A(rawValue: A(value: "something"))
> static let nothing = A(rawValue: A(value: "nothing"))
> }
>
> let value = Test.something
>
> switch value {
>
> case .something:
> // handle
>
> case .nothing:
> // handle
>
> // Because of `SomeFancyName` the switch can use enum-like pattern matching +
> does not need the `default` case when all cases are present
> }
>
>
>
> --
> Adrian Zubarev
> Sent with Airmail
>
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