Re: Fastest way to check using if identifier has already been defined, using static if or similar?

[Basile B. via Digitalmars-d-learn]

On Wednesday, 3 June 2020 at 10:24:44 UTC, Simen Kjærås wrote:
On Wednesday, 3 June 2020 at 09:39:34 UTC, Basile B. wrote:
You can use this template:
  enum Exists(alias T) = is(typeof(T));

I don't know if there's a faster way bu this technic is used, 
notatbly in phobos, to workaroud issues of double declaration 
in `static foreach`

enum Exists(alias T) = is(typeof(T));
static assert(!Exists!bar); // undefined identifier bar

--
  Simen

This is because the template parameter must be resolved to a 
valid symbol or type.
This version other version bypass the problem:

---
enum Exists(string s) = is(typeof(mixin(s)));

void main()
{
    static if (!Exists!"foo")
        int foo;
    foo = 42;
}
---