Use const enum values in enum declarations member initializer.

[mpawelski]

Right now we can write code like this in C#:

enum EnumA
    {
        Foo = 1
    }

    enum EnumB
    {
        Foo = EnumA.Foo,
        Bar = 1
    }

and in Typescript we can simulate that with this code:

enum EnumA {
    Foo = 1
}

enum EnumB {
    Foo = <number>EnumA.Foo,
    Bar = 1
}

and everything work fine (just EnumB.Foo isn't inlined, but it is not a big problem).

It would be nice if we could do something like this with const enums:

const enum EnumA {
    Foo = 1
}

const enum EnumB {
    Foo = EnumA.Foo,
    Bar = 1
}

It would be similar to what we can do right now in C# enums. Personally, want this feature because I want my declared enums in TypeScript (API client) to be exactly like those in C# code (API server), but I think it would be useful for others too. Besides, current error In 'const' enum declarations member initializer must be constant expression. is a little funny because cons enum values are constant expressions in mu opinion ;)

[RyanCavanaugh]

Seems reasonable to add "previously-declared const enum members" the list of things we consider valid for const enum member initializers

[vladima]

Agree, this looks like a nice change to make

[ghost]

I think this should be closed?

[RyanCavanaugh]

Seems so.