What is the complexity of this LINQ example?

Question

I'm curious about the overall LINQ performance. I admit this will come in handy, but how does LINQ work? I know this is a broad question. So I want to ask about a specific example:

I have an anonymous type:

var users = reader.Select(user => new MembershipUser(reader.Name, reader Age));

And now I want to convert it to MembershipUserCollection.

So, I do it like this:

MembershipUserCollection membershipUsers = new MembershipUserCollection();
users.ToList().ForEach(membershipUsers.Add); //what is the complexity of this line?

What is the complexity of the last line? Is it n ^ 2?

Does the ToList () method iterate for each user item and add it to the list? Or does ToList () work differently? Because if this is not so, I can hardly judge the reason for using the last line of code, and not just:

foreach (var user in users)
{
    membershipUsers.Add(user);
}

Answer 1

It O (n) - .ToList() List<T> ( O (1)). , .

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foreach (var user in users) membershipUsers.Add(user)

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Answer 2

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Answer 3

​​ , , , , . - O (n).

The performance of using ForEach in the list compared to the foreach loop comes down to the overhead of calling a delegate and the overhead of creating and using an enumerator, I can’t say which one is faster, but if both are used in the -memory list, the complexity is the same .