How does IEnumerable work in background

Question

I am wandering about the more in-depth functionality of the IEnumerable interface.

Basically, it works as an intermediary step in execution. Fo

Answer 1

So, what is the collection the actual items (in the example 2*x items) reside in?

It is not residing anywhere. There is code that will produce the individual items "on demand" when you iterate, but the 2*x numbers are not computed upfront. They are also not stored anywhere, unless you call ToList or ToArray.

Moreover, if we were to write IEnumerable temp = Enumerable.Repeat(1, 10);, what would be the underlying collection where the 1s are stored (array, list, something else)?

The same picture is here: the returned implementation of IEnumerable is not public, and it returns its items on demand, without storing them anywhere.

C# compiler provides a convenient way to implement IEnumerable without defining a class for it. All you need is to declare your method return type as IEnumerable, and use yield return to supply values on as-needed basis.