Programming C#, Second Edition

Chapter 6. Operator Overloading

It is a design goal of C# that user-defined classes have all the functionality of built-in types. For example, suppose you have defined a type to represent fractions. Ensuring that this class has all the functionality of the built-in types means that you must be able to perform arithmetic on instances of your fractions (e.g., add two fractions, multiply, etc.) and convert fractions to and from built-in types such as integer (int). You could, of course, implement methods for each of these operations and invoke them by writing statements such as:

Fraction theSum = firstFraction.Add(secondFraction);

Although this will work, it is ugly and not how the built-in types are used. It would be much better to write:

Fraction theSum = firstFraction + secondFraction;

Statements like this are intuitive and consistent with how built-in types, such as int, are added.

In this chapter you will learn techniques for adding standard operators to your user-defined types. You will also learn how to add conversion operators so that your user-defined types can be implicitly and explicitly converted to other types.

Using the operator Keyword

In C#, operators are static methods whose return values represent the result of an operation and whose parameters are the operands. When you create an operator for a class you say you have “overloaded” that operator, much as you might overload any member method. Thus, to overload the addition operator (+) you would write:

public static Fraction ...