Using foreach in c#

Question

I read about IEnumerable:

IEnumerable or IEnumerable<T> : by implementing this an object states that it can give you an iterator that you can use to traverse over the sequence/collection/set

So, the foreach statement uses only the IEnumerable interface to iterate over a collection ?

Or does it use IEnumerator too ?

Answer 1

IEnumerable exposes a single method, which returns an IEnumerator. So, the answer is: it uses both.

Answer 2

IEnumerator does not expose GetEnumerator so a foreach will throw an error.

IEnumerable numbers = new[]{1,2,3,4,5};
foreach(var number in numbers) //finds GetEnumerator()
{
    Console.WriteLine(number);
}

IEnumerator numbers2 = new[]{1,2,3,4,5}.GetEnumerator();
foreach(var number in numbers2) //cannot find GetEnumerator, throws
{
    Console.WriteLine(number);
}

The second foreach will throw an error because foreach is specifically looking for the GetEnumerator method which is not exposed on IEnumerator its self.

Answer 3

If you look at the IEnumerable interface, you will find out that its only method is to get IEnumerator to iterate.