Operator overloading can be misused and abused. Here is a quick review of some of the operator overloading guidelines discussed so far in this course.

Operator overloading is easily misused. Do not overload operators when such overloading can lead to misinterpretation. The domain of use should have a widely used notation that conforms to your overloading.
Overload related operators in a manner consistent with C++ community expectations. For example, the relational operators <, >, <=, and >= should all be meaningful and provide expected inverse behaviors.

Generally speaking, you should overload symmetrical binary operators, such as +, *, ==, !=, and && with friend functions. Both arguments are then passed as ordinary parameters. This subjects both arguments to the same rules of parameter passing. Recall that using a member function to provide overloading for symmetrical binary operators causes the first argument to be passed via the this pointer.

Any time a class uses new to construct objects, it should provide an explicitly overloaded operator=(). This advice is analogous to our rule that such a class provide an explicit copy constructor. The compiler-provided default assignment operator semantics would in most cases give spurious behavior. This leads to a suggested normal form for classes with heap-managed memory.

//Normal Form for heap managed classes illustrated
class vect {
public:
    vect();                     //default constructor
    vect(const vect&);         //copy constructor
    .....
    vect& operator=(const vect&); //returns lvalue
    .....
};

This normal form rule applies as well to reference counted classes, such as the string type. The reason the operator=() returns a reference is to allow assignment to work efficiently. This requires lvalue semantics.

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