C# Linq question

Question

If I have the following statement:

whatever.Select(x => collection.ToArray()[index]).ToList();

So, is the LINQ smart enough to perform the ToArray cast only once (I'm not really aware of how this closure is transformed and evaluated)?

I understand this code is bad, just interested.

Answer 1

不，它会在任何每个项目进行一次。

Answer 2

You can have a peek at the code for LINQBridge , especially the Select method (that ends up calling SelectYield .

The essence of SelectYield is a simple for-loop:

foreach (var item in source)
    yield return selector(item, i++);

Where selector is the lambda expression you pass in, in your case x => collection.ToArray()[index] . From here it is obvious that the whole lambda expression will be evaluated for every element in whatever .

Note that LINQBridge is a stand alone reimplementation of LINQ2Objects and thus not necessarily identical (but to a very large extent at least behaving exactly like LINQ2Objects, including side effects).