IEnumerable<T>
Learn the iterable collection contract with IEnumerable<T>.
The IEnumerable<T> contract
IEnumerable<T> is the contract for any sequence you can walk with foreach. It requires a single member: the GetEnumerator() method, which returns an IEnumerator<T>.
List<T>, T[] and Queue<T> all implement IEnumerable<T>. A method accepting IEnumerable<int> takes any of them. This makes swapping collections easy.
GetEnumerator and foreach
When you write foreach (var x in seq) the compiler calls seq.GetEnumerator() behind the scenes. The loop calls MoveNext() each step and reads the Current property. When MoveNext returns false the loop stops.
So foreach is a shortcut for explicitly calling IEnumerator members. A class implementing IEnumerable<T> works with foreach automatically, no extra code needed.
Exercise Write an IEnumerable<int> method
Write a PrintAll(IEnumerable<int> items) method that prints each item with foreach and Console.WriteLine. Add a PrintAll(list) call in Main.
Show example solution
In PrintAll iterate items with foreach, print each with WriteLine. Add PrintAll(list); in Main.
Example solution:
using System;
using System.Collections.Generic;
class Program
{
static void PrintAll(IEnumerable<int> items)
{
foreach (var item in items)
{
Console.WriteLine(item);
}
}
static void Main()
{
var list = new List<int> { 1, 2, 3 };
PrintAll(list);
}
}Test yourself
-
What does IEnumerable<T> provide?
- foreach iteration
- Indexed access
- Thread safety
- Automatic sorting
Show answer
foreach iteration — Correct. Types implementing IEnumerable<T> can be iterated with foreach.
-
Implement the interface
class Bag : IEnumerable<____>Show answer
class Bag : IEnumerable<int> -
Match the member to its role
- GetEnumerator
- Returns iterator
- MoveNext
- Advances to next
- Current
- Current item
- Reset
- Returns to start