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by joe_guy 1675 days ago
Do you know why that is? That's very interesting.
2 comments
sbelskie 1675 days ago
Not sure if it is still the case, but it used to be that First did a fairly naive foreach over the IEnumerable while Where has several collection specific type checks that allow it to use MoveNext and maybe other more efficient ways to traverse the collection.
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foepys 1675 days ago
LINQ is parsing a tree of System.Linq.Expression here and the cases of First(pred) etc. are just not optimized because of the added complexity with little benefit. It only recently became a problem when Visual Studio got a new built-in analyzer that tells people to "optimize" this.
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sobani 1674 days ago
If you're using LINQ on a list, it will not use Expressions, but a plain Func. So nothing will get parsed either way.

The difference, as @sbelskie already mentioned, is that Where has an optimization for List, while First only uses the naive enumerator.

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