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digitalmars.D - Template type deduction and specialization works on template alias

I just wanted to make this post to showcase that template type 
deduction and template specialization works on templates alias 
parameters and give an example of what this could possibly be 
used for.

```
struct Identity(A)
{
     A get;
}

f!B fmap(alias f : Identity, A, B)(B delegate(A) callback, f!A 
functor)
{
     return Identity!B(callback(functor.get));
}

struct Array(A)
{
     A[] get;
}

f!B fmap(alias f : Array, A, B)(B delegate(A) callback, f!A 
functor)
{
     B[] result = new B[functor.get.length];
     foreach (c, ref x; result)
     {
         x = callback(functor.get[c]);
     }
     return Array!B(result);
}

f!int square(alias f)(f!int functor)
{
     return fmap((int x) => x * x, functor);
}

void main()
{
     import std.stdio;

     auto one = fmap((int a) => a + 1, Identity!int(0));
     auto numbers = fmap((int a) => a + 1, Array!int([1, 2, 3]));

     one.writeln;
     numbers.writeln;

     Identity!int(4).square.writeln;
     Array!int([1, 2, 3]).square.writeln;
}
```
Oct 24