Question

Is it necessary that the assignment operator (=) always copies the rvalue into the lvalue or is it completely dependent on the type of operands that it is operating on? Sorry if it is silly but whatever I read, it is written that it just copies the value on the right to the left. I want to get my facts right.

Please give an example in C++.

Answer 1

Is it necessary that the assignment operator (=) always copies the rvalue into the lvalue.

No. For user-defined types it does no such thing. Rather, it invokes the appropriate operator= function. Consider these classes:

#include <iostream>
struct Half {
  int i;
  void operator=(int j) { i = j/2; }
};
struct Double {
  int i;
  void operator=(int j) { i = j*2; }
};
int main () {
  Half h;
  h = 3;
  Double d;
  d = 3;
  std::cout << h.i << " " << d.i << "\n";
  // Result is "1 6"
}

As you can see, the assignment operator is free to perform whatever actions it sees fit. In this case, it is clearly not merely a “copy”.