Lesson 16	Tips for overloading operators
Objective	Learn safe and consistent guidelines for operator overloading in modern C++.

Overloading Operators in C++

Operator overloading can make user-defined types feel natural, but it is also one of the most abused features of C++. Use it only when it improves clarity, aligns with community expectations, and preserves semantic correctness. Avoid "clever" overloads that surprise readers or obscure intent.

When Not to Overload Operators

Do not overload operators if the meaning will confuse readers or deviate from mathematical or established C++ practice. For example:

A type Matrix may reasonably overload + to add matrices, but overloading ^ to mean matrix exponentiation is non-standard and misleading.
All relational operators (<, >, <=, >=) should be consistent with one another and with ==/!=.
Overload only if there is a natural, widely recognized notation for the operation in your problem domain.

Symmetric Operators and `friend` Functions

Symmetric binary operators such as +, *, ==, !=, and << are often best implemented as non-members. When those functions need access to private state, declare them as friend inside the class. This ensures both operands are treated equally and avoids surprises with implicit conversions.


#include <ostream>
class Vector {
  double x_, y_;
public:
  Vector(double x, double y) : x_{x}, y_{y} {}
  // hidden friend for symmetry
  friend Vector operator+(const Vector& a, const Vector& b) {
    return Vector{a.x_ + b.x_, a.y_ + b.y_};
  }
  friend std::ostream& operator<<(std::ostream& os, const Vector& v) {
    return os << '(' << v.x_ << ", " << v.y_ << ')';
  }
};

Overloading Assignment in Heap-Managed Classes

If a class allocates resources (e.g., with new, raw file handles, sockets), it must follow the Rule of Three/Five/Zero. Provide a custom copy constructor, copy assignment operator, and destructor (and in modern C++, consider move constructor and move assignment too).


// Modern normal form for resource-managing classes
class Vect {
public:
    Vect();                               // default constructor
    Vect(const Vect&);                    // copy constructor
    Vect& operator=(const Vect&);         // copy assignment (returns lvalue ref)
    Vect(Vect&&) noexcept;                // move constructor
    Vect& operator=(Vect&&) noexcept;     // move assignment
    ~Vect();                              // destructor
private:
    double* data_;
    std::size_t size_;
};

Returning by reference from operator= is essential to support chaining:

a = b = c;

Classes like std::string and std::vector follow this pattern. Modern C++ encourages RAII and smart pointers (std::unique_ptr, std::shared_ptr) to minimize the need for manual overloads.

Additional Modern Guidelines

Prefer defaulted special members when raw resource ownership is not involved. Let the compiler generate safe defaults.
Ensure noexcept correctness: If your assignment or swap cannot throw, mark it noexcept. This improves performance in containers.
Define related operators together: If you overload <, consider also defining >, <=, >=, or use =default with C++20’s <=> operator.
Avoid gratuitous overloads: Just because you can overload ++ for a class does not mean you should. Use only if the semantics match the operator’s traditional meaning.
Document intent: Operator overloads are terse by nature; comments or references to domain math help maintain readability.

Mathematical ADT - Quiz

Click the Quiz link below to take a brief multiple-choice quiz on operator overloading.
Mathematical ADT - Quiz