[swift-evolution] [Review] SE-0023 API Design Guidelines

[Trent Nadeau]

I should clarify. I mean that they're like types in that they have a unique
scoped name with fields. A union with cases with associated values is a sum
types of product types. Obviously, they can't be used like "real" types as
formal parameters, etc.

I don't see them as values or initializers but very constrained types. For
instance, in C you could have something like:

struct Foo {

    int tag;


    union {

        struct Bar {

           int x;

           int y;

        } bar;



        struct Baz {

          double a;

          double b;

        } baz;

    } data;

};

which would be equivalent to Swift's:

enum Foo {
    case Bar(x: Int, y: Int)
    case Baz(a: Double, b: Double)
}

Bar and Baz in the C code above are actual types just unusable outside of
the sum type (tagged union). If that's not similar to Swift, please correct
me.

On Tue, Jan 26, 2016 at 2:02 PM, Dave Abrahams via swift-evolution <
swift-evolution at swift.org> wrote:

>
> on Sun Jan 24 2016, Thorsten Seitz <swift-evolution at swift.org> wrote:
>
> > Yes, I think they are a lot like sum (or union) types. In Ceylon enums
> > actually are modeled as union types (there is no specific enum
> > syntax).
>
> Enums in Swift are exactly that; Ceylon chose the name "union;" we chose
> "enum."  But Trent is saying that enum *cases* are like types.
>
> > -Thorsten
> >
> >> Am 23.01.2016 um 19:57 schrieb Trent Nadeau via swift-evolution
> >> <swift-evolution at swift.org>:
> >>
> >> While enum cases may not be types from a compiler perspective, I think
> they are from a user's level.
> >>
> >> Consider:
> >>
> >> enum MyError: ErrorType {
> >>     case FileError(fileName: String)
> >>     case SocketError(ipAddr: String, port: Int16)
> >> }
> >>
> >> From a compiler perspective, it's a tagged union (one type), but for
> >> a user this is a set of disjoint types that happen to share the same
> >> space and have exhaustiveness checking, etc. It's a much more
> >> efficient and convenient version of multiple structs or tuples.
> >>
> >> On Sat, Jan 23, 2016 at 1:49 PM, Joe Groff
> >> <jgroff at apple.com
> >> <mailto:jgroff at apple.com>> wrote:
> >>
> >> > On Jan 23, 2016, at 10:24 AM, Trent Nadeau
> >> > <tanadeau at gmail.com
> >> > <mailto:tanadeau at gmail.com>> wrote:
> >> >
> >> > I think it makes sense for enum cases to be UpperCamelCase as they
> >> > can be thought of as scoped types (singleton types in the case of
> >> > cases with no associated types).
> >>
> >> They aren't, though. I don't see much value in setting false
> expectations.
> >>
> >> -Joe
> >>
> >>
> >>
> >>
> >> --
> >> Trent Nadeau
> >> _______________________________________________
> >> swift-evolution mailing list
> >> swift-evolution at swift.org
> >> https://lists.swift.org/mailman/listinfo/swift-evolution
> >
> > _______________________________________________
> > swift-evolution mailing list
> > swift-evolution at swift.org
> > https://lists.swift.org/mailman/listinfo/swift-evolution
>
> --
> -Dave
>
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>



-- 
Trent Nadeau
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