Allow parameterized enum declaration

[dlangBugzillaToGithub]

Kenji Hara (@9rnsr) reported this on 2013-08-13T08:49:37Z

Transferred from https://issues.dlang.org/show_bug.cgi?id=10818

CC List

• Walter Bright (@WalterBright)
• Adam Wilson

Description

Aggregate declarations could have optional template parameters.

class C1 {}
class C2(T) {}

interface I1 {}
interface I2(T) {}

struct S1 {}
struct S2(T) {}

union U1 {}
union U2(T) {}

Similarly, parameterized enum declaration would increase language consistency.

enum E1 {}
enum E2(T) {}
enum E2(T) if (constraint) {}
enum E2(T) : T {}
enum E2(T) if (constraint) : T {}
enum E2(T) : T if (constraint) {}

[dlangBugzillaToGithub]

k.hara.pg commented on 2013-08-13T09:17:14Z

https://github.com/D-Programming-Language/dmd/pull/2474

[dlangBugzillaToGithub]

bugzilla (@WalterBright) commented on 2013-08-16T20:48:24Z

Are there any existing use cases that this would improve?

[dlangBugzillaToGithub]

k.hara.pg commented on 2013-08-16T22:57:47Z

(In reply to comment #2)
> Are there any existing use cases that this would improve?

I don't have actual use case. I'm proposing this enhancement just for increasing language consistency.

---

Now I'm opening a compiler PR to extend DIP42 feature.
https://github.com/D-Programming-Language/dmd/pull/2467

This is necessary to support `enum bool x(T) = initializer` syntax, and looks to me it is very similar to N3651 in C++14.
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3651.pdf

After #2467 is accepted, we would could make most of declarations parameterize - aggregates, functions, and variable declarations.

And, at that time enum declaration would be remained just one declaration which cannot be parameterized. That would be inconsistent.