> On 20 Feb 2017, at 06:40, Niels Andriesse via swift-evolution
> <swift-evolution@swift.org> wrote:
>
> I'd like to discuss the possibility of treating the cases of a given enum as
> if they are subtypes of that enum. This seems like a natural thing to do
> because enum cases (especially when they have associated values) effectively
> define a closed set of subtypes.
>
> Doing so would allow for constructions such as the following:
>
> enum Foo {
> case a(name: String)
> }
>
> func isA(foo: Foo) -> Bool {
> // The old way:
> if case .a = foo { return true }
> return false
> // The new way:
> return foo is .a
> }
>
> func printNameIfFooIsA(foo: Foo) -> Bool {
> // The old way:
> if case let .a(name) = foo {
> print(name)
> }
> // The new way (1):
> if let a = foo as? .a {
> print(a.name <http://a.name/>)
> }
> // The new way (2):
> if let name = (foo as? .a)?.name {
> print(name)
> }
> }
>
> Treating an enum's cases as its subtypes would make enums easier to work with
> because handling them would be syntactically the same as handling other types.
>
> The pattern matching capabilities of enums wouldn't be affected by this
> proposal.
>
> Multiple other proposals have already attempted to simplify enum handling
> (they have particularly focused on getting rid of "if case" and adding the
> ability to treat enum case tests as expressions), but none of the solutions
> presented in those proposals have worked out so far.
>
> I believe that this could be the right solution to multiple enum-related
> problems that have been brought up repeatedly.
I really like the simplification of is/as here, since the leading dot should be
clear enough and is consistent with other usages of enums.
Presumably this would apply even further though? For example, could I do:
func myMethod(_ something:Foo.a) -> Foo.a { … }
i.e- take and return only instances of Foo.a?
It should then also be possible for me to do:
let a:Foo = myMethod(Foo.a("test"))
In other words, Foo.a is a valid instance of Foo (but not vice versa without
casting first)?_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution
