Lack support of overload resolution among multiple existing abstractions

[mingxwa]

Consider the following C++ code without using proxy:

struct Base1 {
  virtual void f() = 0;
  virtual ~Base1() = default;
};
struct Base2 {
  virtual void f(int v) = 0;
  virtual ~Base2() = default;
};
struct CombinedBase : Base1, Base2 {};

While both Base1::f() and Base2::f(int) can be called with a single symbol f on a value of type CombinedBase, there is no equivalent facility in the proxy library.