Distinction between iterator and enumerator

Question

An interview question for a .NET 3.5 job is \"What is the difference between an iterator and an enumerator\"?

This is a core distinction to make, what with LINQ, etc

Answer 1

In C# 2+, iterators are a way for the compiler to automatically generate the IEnumerable and/or IEnumerable interfaces for you.

Without iterators, you would need to create a class implementing IEnumerator, including Current, MoveNext, and Reset. This requires a fair amount of work. Normally, you would create a private class that implemtented IEnumerator for your type, then yourClass.GetEnumerator() would construct that private class, and return it.

Iterators are a way for the compiler to automatically generate this for you, using a simple syntax (yield). This lets you implement GetEnumerator() directly in your class, without a second class (The IEnumerator) being specified by you. The construction of that class, with all of its members, is done for you.

Iterators are very developer friendly - things are done in a very efficient way, with much less effort.

When you use foreach, the two will behave identically (provided you write your custom IEnumerator correctly). Iterators just make life much simpler.