Is there an IEnumerable implementation that only iterates over it's source (e.g. LINQ) once

Question

Provided items is the result of q LINQ expression:

var items = from item in ItemsSource.RetrieveItems()
            where ...

Answer 1

Take a look at the Reactive Extentsions library - there is a MemoizeAll() extension which will cache the items in your IEnumerable once they're accessed, and store them for future accesses.

See this blog post by Bart De Smet for a good read on MemoizeAll and other Rx methods.

Edit: This is actually found in the separate Interactive Extensions package now - available from NuGet or Microsoft Download.