Bug 7657 – ReturnType fails for simple templated functions

import std.algorithm; import std.traits; void main() { alias ReturnType!countUntil Type; // fails } Here's the thing: countUntil has a defined return type and it doesn't change based on its template arguments. So I think the above should work. I'm doing some metaprogramming and I need to get the return type of a function so I can wrap it. I can't simply use 'auto' because I'm also wrapping the return type, e.g.: template Magic(alias func) { Wrapped!(ReturnType!func) Magic(T...)(T t) { // .. } } I think ReturnType could be made to work even though it's a non-instantiated template (I'm not sure how but maybe there's a way).

Except that if a template hasn't been initialized, it doesn't even really _exist_ as far as the compiler is concerned. It's a template for something, not an actual function or type. So, while I can see why you'd want this, I just don't see how it could be done with how templates are implemented.

(In reply to comment #1) > Except that if a template hasn't been initialized, it doesn't even really > _exist_ as far as the compiler is concerned. It's a template for something, not > an actual function or type. > > So, while I can see why you'd want this, I just don't see how it could be done > with how templates are implemented. Yes, and come to think of it it would be dangerous to allow this feature. If at a later time a template had its return type changed to 'auto' it would break existing code that relied on ReturnType working on such a template.