On Wednesday, 20 July 2016 at 05:54:41 UTC, mogu wrote:
On Wednesday, 20 July 2016 at 01:50:37 UTC, Adam D. Ruppe wrote:
On Wednesday, 20 July 2016 at 01:14:05 UTC, mogu wrote:
Why S's type isn't something like `S: (T) -> S`?

Because S isn't a type... think of a template as being like a function that returns a type.

int foo(int) { return 0; }

There, you wouldn't expect typeof(foo) to be int, no, typeof(foo) is a function that returns an int.

The template is the same thing - it isn't a type, it is a template that returns a type.

So it's a higher kinded type aka type class in Haskell. But D's reflection cannot get enough information about template's kind. Only a `void` given. It may be inconvenient in distinction between an alias of template and void. The only solution AFAIK is by string of the type property .stringof.

Note that void is a type, while S is not. So you can do:

assert(is(void)) // is(type) returns true
assert(!is(S))   // is(template) returns false;

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