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Return null for FirstOrDefault() on empty IEnumerable<int>?

Answer 1

+10 A:

int? nullableId = GetNonNullableInts().Cast<int?>().FirstOrDefault();

Matt Howells 2009-12-01 10:33:45

Is there no way to define the Default from FirstOrDefault?When the list does return a set of ints, casting them all for no real reason doesn't really look like a good idea to me.

borisCallens 2009-12-01 10:46:30

Cast() does not cast them all - it only casts them as you enumerate. So this code will cast either zero or one ints - not much of a performance hit.

Matt Howells 2009-12-01 12:02:15

You cannot define the default value returned by FirstOrDefault - it returns either the first element from the enumerable, or if none exists, the result of `default(T)`.

Matt Howells 2009-12-01 12:06:16

You are correct, I was confused. Parsing one value is no biggy.

borisCallens 2009-12-01 14:48:28

And if you want to implement FirstOrValue, here's an article on how to do it wrong vs how to do it right: http://stackoverflow.com/questions/1708846/a-different-take-on-firstordefault

Eric Lippert 2009-12-01 14:51:53

Answer 2

A:

FirstOrDefault depends on T from IEnumerable<T> to know what type to return, that's why you're receiving int instead int?.

So you'll need to cast your items to int? before return any value, just like Matt said

Rubens Farias 2009-12-01 10:37:31

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Return null for FirstOrDefault() on empty IEnumerable<int>?

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