CODEWITHSUNDEEP
c#linqresharper
JoeS
JoeS

Reputation: 1425

LINQ and ReSharper

Hi I have the following code:

if (!_jobs.Any(j => j.Id == emailJob.Id))
{
}

This code should find any elements which satisfy the condition. So I would assume that it should return after finding the first element, something like this:

if (!_jobs.FirstOrDefault(j => j.Id == emailJob.Id) != null)
{
}

Resharper tries to simplify this LINQ expression to:

if (_jobs.All(j => j.Id != emailJob.Id))
{
}

This seems less efficient to me because it has to check that every single element satisifies the inverse condition.

Sorry if I'm just misunderstanding how LINQ works.

Joe

Upvotes: 2

Views: 582

Answers (3)

Nick Freeman
Nick Freeman

Reputation: 1411

Both Any and All will stop looking immediately upon the condition failing.

If you are looking for more than just taking our word or anecdotal evidence, you can see from the source that this is what it is doing.

Decompiled Any and All methods

There is an extra inversion in the All method after the predicate is applied. This is a relative 0 performance impact, so code readability is the main concern.

Upvotes: 3

recursive
recursive

Reputation: 86074

If there is any job that does match the emailJob id, then the .Any() approach can abort early. By the same token, the .All() approach can stop working as soon as it finds a condition that's false, which will happen at the same job. The efficiency should be about the same.

Upvotes: 1

Jon
Jon

Reputation: 437356

The two versions are mirror approaches and do exactly the same amount of work.

When you say "if none of the items satisfy this condition" (!Any), then all of the items have to be checked in order to get a definite answer.

ReSharper's suggestion is useful because it guides you towards using the method that more clearly shows what is going to happen: All jobs will have to be examined.

Upvotes: 7

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