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c#linqwhere-clause
jasonh
jasonh

Reputation: 30293

LINQ results when there are no matches?

What exactly does a LINQ function return when there are no matches? Take the Where method, for example:

var numbers = Enumerable.Range(1, 10);
var results = numbers.Where(n => n == 50);

What would be in results at this point?

Upvotes: 10

Views: 8604

Answers (3)

Jon Skeet
Jon Skeet

Reputation: 1499800

results itself is just a query. Until you start to iterate through it (either explicitly or via a call like Count()), nothing has checked whether there are any results or not. It's only when you enumerate it that anything will happen.

So you could do:

foreach (int x in results)
{
    Console.WriteLine("This won't happen");
}

Or:

Console.WriteLine(results.Any()); // Will print false
Console.WriteLine(results.Count()); // Will print 0

Any of these will cause the predicate to be evaluated against each item in the range... but before then, it won't be called at all.

This is an important thing to understand, because it means that results couldn't be null while retaining the feature of lazy evaluation - until you tried to use results, it wouldn't have worked out whether it should be null or not!

Upvotes: 12

Quintin Robinson
Quintin Robinson

Reputation: 82325

A reference to an empty IEnumerable<T>.

Upvotes: 3

Ahmad Mageed
Ahmad Mageed

Reputation: 96477

In this case it returns an IEnumerable<Int32> with a count of 0 items.

Upvotes: 4

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