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Lesson 16 Tips for overloading operators
Objective Review some operator overloading guidelines.

Overloading Operators in C++

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.

When not to overload C++ Operators

Operator overloading is easily misused, so 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.

Use friend Functions

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.

Overloading Assignment with new

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 {
    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.

Mathematical ADT Quiz

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