Constraining template with function signature

[Carl Vogel via Digitalmars-d-learn]

On Thursday, 9 June 2016 at 19:08:52 UTC, cy wrote:
> But it's probably clearer to use that is(typeof({ how this 
> function will be called })) trick.

A very delayed thanks to both of you. It does seem like it would 
be useful to have something like a hasSignature!(Fun, Ret, 
Args...) defined in std.traits. But Steven's solution is pretty 
good.

Thanks again!