More Operator Overloading

Automatic type conversion and explicit

Implicit type conversion

Type conversion and classes

• The existence of a 1-argument constructor implies the ability to do a type conversion.
• By default, the compiler will apply the conversion if needed when doing assignments and parameter matching.
• To disallow these implicit type conversions, designate the 1-argument constructor with the keyword explicit

General guideline: 1-argument constructors should be explicit unless there is a good reason to allow implicit type conversions.

Example: Suppose we remove explicit from the 1-argument constructor in the Polynomial class. Consider the following code:

Polynomial p1;

Polynomial p2 = 4.1;

p1 = 3.2;

p2 += 8.7;

Polynomial p3;

p3 = p2 + 4.2;
 
p1 = 6.5 + p3;

Member vs Non-Member Revisited

Overloading operatorX

• non-member function: lhs X rhs → operatorX(lhs, rhs)

• member function: lhs X rhs → lhs.operatorX(rhs)

• for member functions, the type of lhs must match exactly (no type conversion)

Suppose + was a member function of the Polynomial class. Consider the following (where p is a Polynomial):

Problem with non-member functions:

Solution 1:

Solution 2:

friend keyword

A friend can

A class can be friends with

How friendship is declared:

Friendship is not:

• inherited
• transitive
• reciprocal

Use with caution! Use a member function when you can and a friend function when you have to.

Overloading relational operators

Convention:

Make sure to be consistent: