Learning C# 3.0

Designing the Fraction Class

For example, suppose you define a type to represent fractional numbers; you might reasonably name it Fraction. The following constructors establish two Fraction objects, the first representing 1/2 and the second representing 3/4:

Fraction firstFraction = new Fraction(1,2); // create 1/2
Fraction secondFraction = new Fraction(3,4); // create 3/4

It’s reasonable to create this class so that the first parameter will represent the numerator and the second parameter will represent the denominator. In general, when you create your classes, you should stick to an obvious and intuitive interpretation whenever you can.

If you want your Fraction class to have all the functionality of the built-in types, you’ll need to be able to perform arithmetic on instances of your fractions (add two fractions, multiply them, and so on). You should also be able to convert fractions to and from built-in types, such as int.

Hypothetically, you could implement methods for each of these operations. For example, for your Fraction type, you might create an Add() method, which you would invoke like this:

// add 1/2 and 3/4
Fraction theSum = firstFraction.Add(secondFraction);

This works just fine, but it’s not very obvious. It’s hard to read, and it’s not how the user would automatically expect addition to work. It also doesn’t look like addition of the built-in types, such as int. It would be much better to be able to write:

// add 1/2 and 3/4 using + operator Fraction theSum = firstFraction ...