LINQ · interview question

What happens when you call First() and FirstOrDefault() on an empty List<string>?

Multiple choiceMedium

`First()` throws InvalidOperationException; `FirstOrDefault()` returns null.Both return null.Both throw InvalidOperationException.`First()` returns an empty string; `FirstOrDefault()` returns null.

Answer and explanation

Correct answer

A. First() throws InvalidOperationException; FirstOrDefault() returns null.

Why

Use First() when an empty sequence is a bug (fail fast). Use FirstOrDefault() when "none" is a valid outcome, and check for default.

References

Microsoft Learn: Language Integrated Query (LINQ)

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