Learning C# 3.0

Conversion Operators

As you learned back in Chapter 3, C# will convert (for example) an int to a long implicitly but will only allow you to convert a long to an int explicitly. The conversion from int to long is implicit because you know that any int will fit into a long without losing any information. The reverse operation, from long to int, must be explicit (using a cast) because it is possible to lose information in the conversion:

int myInt = 5;
long myLong;
myLong = myInt;        // implicit
myInt = (int) myLong;  // explicit

It would certainly be useful to convert your Fraction objects to intrinsic types (such as int) and back. Given an int, you can support an implicit conversion to a fraction because any whole value is equal to that value over 1 (15 == 15/1).

Given a fraction, you might want to provide an explicit conversion back to an integer, understanding that some information might be lost. Thus, you might convert 9/4 to the integer value 2 (truncating to the nearest whole number).

Tip

A more sophisticated Fraction class might not truncate, but rather round to the nearest whole number. Again, we’re trying to keep this example simple, but feel free to implement a more sophisticated method.

To implement the conversion operator, you still use the keyword operator, but instead of the symbol you’re overriding, you use the type that you’re converting to. For example, to convert your Fraction to an int, you’d do this:

public static implicit operator Fraction( int theInt )

You use the keyword ...