Get return type of a template function without instantiating it

[Meta via Digitalmars-d-learn]

On Tuesday, 22 November 2016 at 12:21:18 UTC, Yuxuan Shui wrote:
> Is there a way to get a template function return type with 
> instantiating it? The return type is independent of the 
> template arguments.
>
> I'm asking because there's potentially recursive template 
> instantiation if I do try to instantiate it.

What you want cannot work in the general case. The template 
function must be instantiated.

T identity(T)(T t)
{
     return t;
}

It's not possible to calculate the type of the return value of 
`identity` until it is instantiated with a type.