On Monday, 23 April 2012 at 12:25:21 UTC, Peter Alexander wrote:
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.
I think you've misunderstood the poster as "cond ? a : b" must
fold and Eval(alias arg) receives a compile time value. That
makes it no different from doing just enum al = cond ? a: b;
Which brings us to an interesting point that alias and enum
should be brought together:
alias x = 1;
alias y = int;
should replace current
enum x = 1;
alias int y;
respectively. This is makes it a consistent syntax and behavior
for alias declarations(no reverse order compared to normal
assignments which is a legacy of C's typedef) and also fixes enum
storage class which name is not relevant anymore.
