std.traits.ParameterIdentifierTuple producing empty results.

[Nick Treleaven]

On Tuesday, 2 April 2024 at 00:28:50 UTC, Carl Sturtivant wrote:
> I looked into `is()` with `__parameters` and the documentation 
> is a bit sparse, however eventually I found that I could 
> extract the parameter names without CTFE provided I avoided 
> stripping them out through instantiating a template with them

I realized there's another way, inspired by your `extern 
FunctionType` idea:

```d
import std.traits;

void foo(int i, char c);

void main()
{
     pragma(msg, ParameterIdentifierTuple!foo); // i, c
     alias Foo = typeof(foo);
     pragma(msg, ParameterIdentifierTuple!Foo); // no identifiers
     static if (is(Foo PS == __parameters))
         void f(PS);
     pragma(msg, ParameterIdentifierTuple!f); // i, c
}
```