Operator Overloading: Member Functions vs. Friend Functions – When Should You Choose Which?

Operator Overloading: When to Use Member Functions vs. Non-Member Functions

In operator overloading, asymmetry arises when an operator is declared as a member function, as it requires a single parameter and implicitly passes the this pointer as the other operand. This asymmetry limits comparisons between overloaded operators. On the contrary, friend functions allow for symmetric overloading by passing two arguments of the same type, enabling comparisons.

However, despite the ability to compare pointer lvalues with references, why are friend functions preferred?

Firstly, member function overloading faces an ordering issue when the first operand is not a class type. For instance, expressions like 10.0 s2 are invalid using member function overloading.

To address this, non-member friend functions can be used when accessing private members or when the ordering issue arises. By making the overloaded function a friend of the class, it can access private members, allowing flexibility in operator overloading. However, it is recommended to use non-friend non-member functions to enhance encapsulation unless private member access is required.

In summary, friend functions provide symmetry and address the ordering issue in operator overloading. They offer more flexibility by enabling access to private members, while non-friend non-member functions maintain encapsulation. STL algorithms rely on symmetric versions to avoid ordering complications and maintain consistency in operator usage.

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