Alias Expressions

[Peter Alexander]

On Monday, 23 April 2012 at 03:17:49 UTC, Xinok wrote:
> I know this has probably been asked for a hundred times before, 
> but I don't understand why D doesn't support this. Template 
> alias parameters can accept nearly anything as an argument that 
> standard aliases don't. I think standard aliases should be 
> equally as powerful as their template counterpart.
>
> If you can write this:
> template Eval(alias arg){ alias arg Eval; }
> alias Eval!(cond ? a : b) al;
>
> Why not simply allow this?
> alias (cond ? a : b) al;
>
> Or perhaps this:
> alias al = cond ? a : b;

Do equivalent expressions instantiate the same template?

class Foo(alias E) {}
int x, y;
alias (x + y) A;
alias (x + y) B;
alias (y + x) C;

Are Foo!A and Foo!B the same type? What about Foo!C?

Either way, it will require name-mangling of arbitrary 
expressions, which is just plain nasty.