• dennis luehring (8/8) Aug 04 2007 how can i get the element type of an array at compiletime?
• Frits van Bommel (44/54) Aug 05 2007 (This sort of post is more appropriate in digitalmars.D.learn, followups...
• Christian Kamm (17/18) Aug 05 2007 For dynamic arrays and associative arrays, something like this would wor...

dennis luehring <dl.soluz gmx.net> writes:

how can i get the element type of an array at compiletime?

example:
   int test[5] --> int
   double test[] --> double

and what is the type of the key of an assoz. array?

   int test[char[]] --> int, char[]
   double test[int] --> double, int

thx

Frits van Bommel <fvbommel REMwOVExCAPSs.nl> writes:

dennis luehring wrote:
 how can i get the element type of an array at compiletime?
 
 example:
   int test[5] --> int
   double test[] --> double
 
 and what is the type of the key of an assoz. array?
 
   int test[char[]] --> int, char[]
   double test[int] --> double, int

(This sort of post is more appropriate in digitalmars.D.learn, followups 
set)

typeof to the rescue:
-----
import std.stdio;

void main() {
     // (typeid is just wrapped around the types to make them printable)

     // Element type of regular arrays: typeof(arr[0]);
     {
         int test[5];
         writefln(typeid(  typeof(test[0])  ));
     }
     writefln();
     {
         double test[];
         writefln(typeid(  typeof(test[0])  ));
     }
     writefln();

     // Assoc. arrays:
     // key type == typeof(arr.keys[0])
     // value type == typeof(arr.values[0])
     {
         int test[char[]];
         writefln(typeid(  typeof(test.values[0])  ));
         writefln(typeid(  typeof(test.keys[0])    ));
     }
     writefln();
     {
         double test[int];
         writefln(typeid(  typeof(test.values[0])  ));
         writefln(typeid(  typeof(test.keys[0])    ));
     }
}
-----
output:
=====
int

double

int
char[]

double
int
=====

Christian Kamm <kamm.incasoftware shift-at-left-and-remove-this.de> writes:

dennis luehring wrote:

 how can i get the element type of an array at compiletime?

For dynamic arrays and associative arrays, something like this would work:

template ArrayElementType(T : T[])
{
  alias T ArrayElementType;
}

template AATypes(T)
{
  // todo: static assert if T is no AA type here

  alias ArrayElementType!(typeof(T.keys)) key;
  alias ArrayElementType!(typeof(T.values)) value;
}

Thinking about it, it's probably simpler to just use

typeof(array[0])
typeof(aa.keys[0]), typeof(aa.values[0]).

Cheers,
Christian