Typeclass instance usage convention about cats HOT 5 CLOSED

I agree with pretty much all of this: I think we should prefer [A: Foo] if the Foo[A] instance is just being routed somewhere else, and (implicit xyz: Foo[A]) if method's on the xyz instance are needed (since even with @inline the Foo.apply call has overhead).

As far as the names of the evidence parameter, I know @tixxit prefers (implicit A: Foo[A]). How do folks feel about that? I often use ev but on reflection I don't think there's really a good reason -- it seems a bit cranky. I guess I don't know showA but unless there are multiple instances it seems verbose.

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(And yes, we do need a contributor guide that spells this out.)

from cats.

I always liked the idea to view the A in (implicit A: Foo[A]) as the companion for the type parameter. But this is only applicable as long as you only have one instance per type parameter. In the case of two or more instances I guess I'd prefer (implicit fooA: Foo[A], barA: Bar[A]).

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shall we close this ticket?

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Yes, I think we have reached broad agreement.

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