Returning References in Copy Assignment

In C++, we return a reference to the object in the copy assignment operator for several important reasons:

Chaining Assignments

Returning a reference allows for chaining of assignment operations. Consider this example:

1#include <iostream>
2
3class Player {
4public:
5  Player& operator=(const Player& other) {
6    // Copy logic here
7    std::cout << "Copying player\n";
8    return *this;
9  }
10};
11
12int main() {
13  Player p1, p2, p3;
14  p1 = p2 = p3; // Chained assignment
15}

1Copying player
2Copying player

Here, p2 = p3 is executed first, then its result (a reference to p2) is used for p1 = p2.

Consistency with Built-in Types

Returning a reference makes the behavior consistent with built-in types. For example:

1int a, b, c;
2(a = b) = c;// This is valid for built-in types

Efficiency

Returning by reference is more efficient than returning by value, as it avoids unnecessary copying of the object.

Enabling Expression Evaluation

Returning a reference allows the assignment to be part of a larger expression:

1#include <iostream>
2
3class Player {
4public:
5  Player& operator=(const Player& other) {
6    // Copy logic here
7    return *this;
8  }
9};
10
11int main() {
12  Player p1, p2;
13  // Assignment as part of condition
14  if ((p1 = p2).isValid()) {
15    std::cout << "Valid player\n";
16  }
17}

Here, we can use the result of the assignment directly in the if condition.

Remember, while returning a reference is the convention and generally the best practice, the language doesn't strictly require it. However, following this convention makes your code more intuitive and consistent with standard C++ practices.