Question

Is there a way I can make my custom class be passed by reference only?

Basically, I have the following class:

class A{
private:
  int _x;
public:
  A(int y){
    _x = y;
  }
};

Can I make it to where I can ONLY pass it by reference? And it will throw a compile time error otherwise?

Answer 1

Several people have suggested making the copy constructor private. This is a mostly good solution to the problem however it’s not complete. It still allows the type itself to accidentally pass itself by value. A more thorough solution is to declare the copy constructor private and then never implement it.

class A{
private:
  // Prevent value copying
  A(const A&);

  int _x;
public:
  A(int y){
    _x = y;
  }
};

Note: As @DeadMG points out, in C++11 using delete is preferred.

A(const A&) = delete;