IEnumerable with expensive resources

Often IEnumerable types allocate scarce resources in GetEnumerator(). For example, the IEnumerator returned from GetEnumerator may hold a reference to an expensive array of Disposable objects. Such IEnumerator types should implement the IDisposable interface to allow explicit cleanup.
internal class ExpensiveEnumerator: IEnumerator, IDisposable{
…
}

public class ExpensiveCollection: IEnumerable{
public IEnumerator GetEnumerator(){
return new ExpensiveEnumerator();
}
…
}

Some languages, for example C# and VB.NET, will call Dispose on enumerators that implement IDisposable when the foreach statement completes.
ExpensiveCollection expensive = new ExpensiveCollection();
foreach(ExpensiveItem in expensiveCollection){
…
} // Dispose will be called on the IEnumerator when the loop terminates