Distinguish recursive Templates

[Manfred Nowak via Digitalmars-d-learn]

How can one determine the recursion depth for templated types?

Example code:

import std.stdio;
class Set(T){
  override string toString(){
    return "Set";
  }
}
void main(){
  auto s0= new Set!uint;
  writeln( s0); // writes Set

  auto s1= new Set!(Set!uint);
  writeln( s1); // should write SetSet
}