Difference in optimization between Linq's OfType<T> and Cast<T>

[IAmTheCShark]

I know what theese methods do under the hood.
What I do not understand here is the fact that Cast<T> has an optimization that checks if the IEnumerable is an IEnumerable<T>.
OfType<T> doesnt do this.

My question is why?

Problem is, that those "redundant" OfType-calls wrap every IEnumerable in a OfTypeIterator which causes optimizations like the ICollection thing in methods like Count() to not work.

[yaakov-h]

This is a question for https://github.com/dotnet/runtime.

[IAmTheCShark]

Whoops, my bad. Ill transfer it there.
#54473