Duck typing (rather than inheritance) in C++

// -*- C++ -*-

#include <string>
#include <iostream>
using namespace std;


struct A {
  int foo() const { return 3; }
  double bar() const { return 3.0; }
};

struct B {
  int foo() const { return 10000; }
  string bar() const { return "B is for BAR"; }
};

template <typename T>
void fn(const T& obj) {
  cout << obj.foo() << " " << obj.bar() << endl;
}


int main() {
  A a;
  fn(a);
  B b;
  fn(b);
  return 0;
}

// Prints:
//
// 3 3
// 10000 B is for BAR
//
// (as you'd hope)