How to: Create an Iterator Block for a Generic List (C# Programming Guide)
In this example the generic class Stack<T> implements the generic interface IEnumerator<T>. An array of the type T is declared and assigned values by using the method Push. In the GetEnumerator method, the values of the array are returned using the yield return statement.
The non-generic GetEnumerator is also implemented, because IEnumerable<T> inherits from IEnumerable. This example shows the typical implementation, which is for the non-generic method to simply forward the call to the generic method.
Example
using System.Collections;
using System.Collections.Generic;
namespace GenericIteratorExample
{
public class Stack<T> : IEnumerable<T>
{
private T[] values = new T[100];
private int top = 0;
public void Push(T t) { values[top++] = t; }
public T Pop() { return values[--top]; }
// These make Stack<T> implement IEnumerable<T> allowing
// a stack to be used in a foreach statement.
public IEnumerator<T> GetEnumerator()
{
for (int i = top; --i >= 0; )
{
yield return values[i];
}
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
// Iterate from top to bottom.
public IEnumerable<T> TopToBottom
{
get
{
// Since we implement IEnumerable<T>
// and the default iteration is top to bottom,
// just return the object.
return this;
}
}
// Iterate from bottom to top.
public IEnumerable<T> BottomToTop
{
get
{
for (int i = 0; i < top; i++)
{
yield return values[i];
}
}
}
//A parameterized iterator that return n items from the top
public IEnumerable<T> TopN(int n)
{
// in this example we return less than N if necessary
int j = n >= top ? 0 : top - n;
for (int i = top; --i >= j; )
{
yield return values[i];
}
}
}
//This code uses a stack and the TopToBottom and BottomToTop properties
//to enumerate the elements of the stack.
class Test
{
static void Main()
{
Stack<int> s = new Stack<int>();
for (int i = 0; i < 10; i++)
{
s.Push(i);
}
// Prints: 9 8 7 6 5 4 3 2 1 0
// Foreach legal since s implements IEnumerable<int>
foreach (int n in s)
{
System.Console.Write("{0} ", n);
}
System.Console.WriteLine();
// Prints: 9 8 7 6 5 4 3 2 1 0
// Foreach legal since s.TopToBottom returns IEnumerable<int>
foreach (int n in s.TopToBottom)
{
System.Console.Write("{0} ", n);
}
System.Console.WriteLine();
// Prints: 0 1 2 3 4 5 6 7 8 9
// Foreach legal since s.BottomToTop returns IEnumerable<int>
foreach (int n in s.BottomToTop)
{
System.Console.Write("{0} ", n);
}
System.Console.WriteLine();
// Prints: 9 8 7 6 5 4 3
// Foreach legal since s.TopN returns IEnumerable<int>
foreach (int n in s.TopN(7))
{
System.Console.Write("{0} ", n);
}
System.Console.WriteLine();
}
}
}
Output
9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 0 1 2 3 4 5 6 7 8 9 9 8 7 6 5 4 3
See Also
Tasks
How to: Create an Iterator Block for a List of Integers (C# Programming Guide)
Reference
Using Iterators (C# Programming Guide)
System.Collections.Generic
IEnumerable