https://www.atnnn.com/p/operator-larrow/

Etienne Laurin
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C++ left arrow operator

Posted on July 29, 2016

Sometimes you have a pointer to a class, and you want to invoke a
method. You can use the -> operator for that.

So what do you do when you have a pointer to a method, and want to
invoke it on a class? Use the <- operator!

 #include <iostream>
  
 template<class T>
 struct larrow {
     larrow(T* a_) : a(a_) { }
     T* a;
 };
  
 template <class T, class R>
 R operator<(R (T::* f)(), larrow<T> it) {
     return (it.a->*f)();
 }
  
 template<class T>
 larrow<T> operator-(T& a) {
     return larrow<T>(&a);
 }
  
 struct C {
     void f() { std::cout << "foo\n"; }    
 };
  
 int main() {
     C x;
     (&C::f)<-x;
 }

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