// This is probably for use in Meta_v2 to get the most efficient
// (read compact) implementation of typical meta scenarios.

interface MutatingMap<A, B> {
  // Non-mutating:
  
    bool isEmpty();
    int size();
    ItIt<Pair<A, B>> iterator();
    bool containsKey(A a);
    B get(A a);
  
  // hashCode/equals, not sure.
  // maybe we shouldn't even have value semantics here
    
  // Mutating:
  
    MutatingMap<A, B> put(A a, B b);
    MutatingMap<A, B> remove(A a);
    MutatingMap<A, B> putAll(Map map);
    MutatingMap<A, B> putAll(MutatingMap map);
    MutatingMap<A, B> clear();
}