Get AA key and value type

[Pierre via Digitalmars-d-learn]

Hi everybody,

I would like to extract key and value type from AA.
I found this answer on forum :

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;
}

But compiler failed,I think T need to be a value in order to get 
keys and values attributes.

So how can I get types without instance ?
Thanks for help.