Attempt to implement type classes without inheritance about cats HOT 11 CLOSED

I seem to recall that the main reason scalaz didn't take this approach was because of the extra overhead of all of the implicit chaining (the extra function calls and instance allocations). I'm not sure how much of a problem this is in practice. Also for what it's worth, I think that I heard @tpolecat say that scalaz has considered taking this approach in scalaz 8.0.

from cats.

I like the idea in principle but I also worry about allocations. Seems like it's worth prototyping.

from cats.

I'm pretty skeptical (as I said on #71). I think the nested field lookups for every single method call will be really bad for performance. I think this strategy is a non-starter for Spire and Algebra.

If we did some testing and found that for Cats it would be OK, then we could move to it, but would have to drop interop with Algebra and Spire. I'm pretty reluctant to do this but willing to talk about it.

from cats.

@non I understand and share your concern regarding the performance of using evidence. I will try to benchmark the two approach at some point.

Should I close this ticket until we have evidence that a non inheritance base approach provide good performance?

from cats.

I just added the "on hold" label. I don't think we need to completely close the issue if it's still under consideration. If it sits here and rots for months then we can close it out.

from cats.

@ceedubs sounds like a plan

from cats.

Sounds good to me too.

from cats.

people are experimenting removing inheritance in scalaz 8:
https://github.com/scalaz/scalaz/blob/37d7c9c8746a1a47f5f05c465f29938654fda838/core/src/main/scala/Order.scala

from cats.

I tried both approaches in the lead up to Scalaz 7, but found it the inheritance free version was unworkable.

def foo[F: Functor]
def bar[F: Monad] = foo // will not typecheck

Adding an "upcasting" implicit from Monad[F] => Functor[F] seems to work until you extend the hierarchy beyond a depth of 2, or, worse, introduce diamonds.

from cats.

@julien-truffaut there hasn't been any discussion on this issue. Do you want to keep it open? Are there concrete proposals to move forward?

from cats.

No we didn't have any discussion regarding this issue recently. So it is better to close it for the moment.

I think scalaz 8 is looking toward this approach, we can always monitor how does it go.

from cats.