#563 – Enumerable Types Can Generate Multiple Enumerators

Each time that the GetEnumerator method in an enumerable type is called, an independent enumerator is generated.  Each enumerator keeps track of its own position in the parent sequence.

In the example below, nested foreach statements each iterate over the same collection.  The outer foreach statement results in one enumerator and the inner foreach statement results in the generation of a new enumerator for each pass of the outer foreach.

In this case, the ability to generate multiple independent enumerators is necessary, so that we can have overlapping foreach statements.

            int[] nums = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

            foreach (int i in nums)
                foreach (int j in nums)
                    Console.WriteLine("{0} x {1} = {2}", i, j, i * j);