How to use map?

[via Digitalmars-d-learn]

On Tuesday, 11 November 2014 at 14:09:43 UTC, Lemonfiend wrote:
> Oh, no it doesn't. My bad.
>
> It was all about !(Foo) vs !(`Foo(a)`). Is there somewhere I 
> can read more about this?

Don't know whether it's documented, but it's a consequence of 
using string mixins.

unaryFun (which is used internally by map) is implemented this 
way:

     auto unaryFun(ElementType)(auto ref ElementType __a)
     {
         mixin("alias " ~ parmName ~ " = __a ;");
         return mixin(fun);
     }

where `fun` is `Foo(a)`. Of course, `Foo` is not visible in 
std.functional. When you pass in a symbol, the lookup work 
because it takes place at the point of instantiation.