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Source Code

The CustomEnumerator project is located under the Chapter 9 subdirectory.

Building Iterator Methods with the yield Keyword

Historically, when you wished to build a custom collection (such as Garage) that supported foreach

enumeration, implementing the IEnumerable interface (and possibly the IEnumerator interface) was

your only option. However, since the release of .NET 2.0, we are provided with an alternative way to

build types that work with the foreach loop via iterators.

Simply put, an iterator is a member that specifies how a container’s internal items should be

returned when processed by foreach. While the iterator method must still be named GetEnumerator(),

and the return value must still be of type IEnumerator, your custom class does not need to imple-

ment any of the expected interfaces.

To illustrate, create a new Console Application project named CustomEnumeratorWithYield

and insert the Car, Radio, and Garage types from the previous example (again, renaming your name-

space definitions to the current project if you so choose). Now, retrofit the current Garage type as

follows:

public class Garage

{

private Car[] carArray = new Car[4];

...