Why does the using statement work on IEnumerator and what does it do?

Question

Back when I was learning about foreach, I read somewhere that this:

foreach (var element in enumerable)
{
    // do something with element
}

is basically equivalent to this:

using (var enumerator = enumerable.GetEnumerator())
{
    while (enumerator.MoveNext())
    {
        var element = enumerator.Current;

        // do something with element
    }
}

Why does this code even compile if neither IEnumerator nor IEnumerator<T> implement IDisposable? C# language specification only seems to mention the using statement in the context of IDisposable.

What does such an using statement do?

Answer 1

Please, check the following link about foreach statement. It uses try/finally block with Dispose call if it's possible. That's the code which is behind using statement.

Answer 2

IEnumerator may not implement IDisposable but GetEnumerator() returns a IEnumerator<T> which does. From the docs on IEnumerator<T>:

In addition, IEnumerator implements IDisposable, which requires you to implement the Dispose method. This enables you to close database connections or release file handles or similar operations when using other resources. If there are no additional resources to dispose of, provide an empty Dispose implementation.

This is of course assuming that your enumeration is an IEnumerable<T> and not just a IEnumerable. If your original enumeration was just an IEnumerable then it wouldn't compile.