Re: compile-time detection of all pointer types in one test

[Andy via Digitalmars-d-learn]

On Sunday, 11 June 2023 at 21:25:21 UTC, DLearner wrote:
Please consider:
```
void main() {
   import std.stdio;

   struct foo {

      int  foo1;
      char foo2;
   }
   foo*   fooptr;

   void*  genptr;


   static if (is(typeof(fooptr) == void*))
             writeln("fooptr is void*");
          else
             writeln("fooptr is not void*");

   static if (is(typeof(fooptr) == foo*))
             writeln("fooptr is foo*");
          else
             writeln("fooptr is not foo*");

   static if (is(typeof(genptr) == void*))
             writeln("genptr is void*");
          else
             writeln("genptr is not void*");
}
```
which produces:
```
fooptr is not void*
fooptr is foo*
genptr is void*
```

Since `void*` variables accept _all_ pointer types, I expected 
to see `fooptr is void*`.

Is there any way of picking up, at compile-time, all pointer 
types in one test?

Use an `is` expression with a parameter list 
(https://dlang.org/spec/expression.html#is-parameter-list):

    void main() {
        import std.stdio;
        struct foo {}
        foo* fooptr;
        static if (is(typeof(fooptr) == T*, T))
                writeln("fooptr is a pointer to a ", T.stringof);
        else
                writeln("fooptr is not a pointer");
    }

As a bonus, you can make use of the pointee type `T`.