Why You Shouldn't Use ToArray or ToList

So if the problem is that ToList *may* cause lazy evaluation, then I think the solution would be to use ToList as close to when you actually need the list as possible, or am I misunderstanding? Thanks for the post, I never thought about the implications of not knowing when ToList would be evaluated.

We *know* that ToList will create a stateful list with eager evaluation. We assume that it will always be this way, and although this is likely to be true, it is still an assumption. I claim the method you use should depend on your intent: if you intend to retrieve an instance of List(T), use ToList(); if you intend to materialize the sequence (causing the sequence to be evaluated), use a Materialize

My argument is as follows :

Assuming your intent is to materialize a sequence and you are using ToList for the implication that the sequence will be materialized.

Using a Materialize method instead:
1) makes your intent clear
2) prevents misinterpretation due to other implications
3) provides one location to change the implementation details for materializing a sequence

Please note this is different than a Memoize function, which isn't as eager. Memoize would cache the results upon evaluation so subsequent traversal will not cause evaluation.

Ah ok, I wasn't sure if you meant that what ToList would actually perform was unclear, or just the developers intention when seeing it in the code. Thanks for the follow up.

I dig a little deeper into it here and introduce memoization: http://www.kodefuguru.com/post/2012/08/13/Caching-LINQ-Results.aspx