Why is .ForEach() on IList and not on IEnumerable? [duplicate]

Answer 1

Just a guess, but List can iterate over its items without creating an enumerator:

public void ForEach(Action action)
{
    if (action == null)
    {
        ThrowHelper.ThrowArgumentNullException(ExceptionArgument.match);
    }
    for (int i = 0; i < this._size; i++)
    {
        action(this._items[i]);
    }
}

This can lead to better performance. With IEnumerable, you don't have the option to use an ordinary for-loop.