CODEWITHSUNDEEP
linqc#-6.0null-propagation-operator
mec
mec

Reputation: 77

Null propagated ?.First() vs .FirstOrDefault()

After using the null propagation operator a while, I stumbled upon writing a linq clause for selecting a single item. Is there a reason (performance, best practice) not to use ?.First()?

MyList?.First();

or

MyList.FirstOrDefault();

Upvotes: 2

Views: 2216

Answers (2)

Thomas Levesque
Thomas Levesque

Reputation: 292575

It's not a question of performance or best practice ; they just don't do the same thing.

MyList?.First() will return null if MyList is null (First() won't even be called thanks to the null propagation operator), and throw an InvalidOperationException if it's empty (because calling First() on an empty list is invalid).

MyList.FirstOrDefault() will throw an ArgumentNullException if MyList is null (because you can't call FirstOrDefault with null), and return null (or the type's default value if it's a value type) if the list is empty.

To handle both cases (MyList is null, MyList is empty), you can do this:

MyList?.FirstOrDefault()

Upvotes: 12

nvoigt
nvoigt

Reputation: 77354

Those two lines simply aren't equivalent.

The first will throw if MyList contains no elements, but not if it's null.

The second will throw if MyList is null, but not if it contains no elements.

Upvotes: 2

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