// Recursive templates - intro to expression templates
// Does absolutely nothing but instantiates templates
#include <iostream>

// operator (no definition what it does :)
struct plus {
  plus() {std::cout<<"adding plus\n";}
};

// node 
template<typename Left, typename Op, typename Right>
class X {
  Left left;
  Right right;
public:
  X(Left l, Right r) : left(l), right(r) { std::cout<<"adding new Left-Op-Right node\n";} 
};

class A {
public:
  template<typename Left, typename Op, typename Right>
  void operator=(X<Left,Op,Right> expression)  {std::cout<<"in = operation\n";}
};


template<typename Left>
X<Left, plus, A> operator+(Left a, A b)
{
  std::cout<<"in  <Left,plus,A>\n";
  return X<Left, plus, A >(a,b);
}

int main()
{
  A a, b, c, d ;
  //std::cout<<a+b+c;// gives error, but shows how the recursion worked
  d=a+b+c;
}