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diesalbla
wants to merge
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typelevel:main
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diesalbla:opaque_transformers_types
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This Pull Request adds a implementation of the monad transformers OptionT, IdT, and Kleisli, for Scala 3. This new implementation uses the new feature of Scala 3, Opaque Types, which may allows us to have them implemented without overhead on the runtime memory.
This may slightly improve performance for libraries that are based on these monad transformers, such as http4s.
Scala-3 comes with its own zero-cost Newtype implementation, as Opaque
Types. This is an improvement over existing case classes, or Newtype
encodings we are using.
In this commit, we bifurcate the `IdT` wrapper in two implementations:
the existing one goes to the Scala-2.x branch, a new one with newtype
is used on the new
This is similar to #3834. I still like the idea, but I remain concerned about the maintenance burden.of two duplicate implementations. Could we mitigate that with some tests that assure compatibility across Scala 2 and Scala 3? Or maybe our test coverage is already sufficient?
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I think this is worth pursuing personally.
I think we should relax our binary compat for scala 3 to be able to merge something like this (as long as we can avoid any special casing in the tests and we expect source compatibility).
I think we should relax our binary compat for scala 3
There's many libraries published for scala 3 already that depends on cats, are they all OK with throwing bincompat out of the window for hypothetical performance benefits? IMO this belongs in a cats 3 branch or in https://github.com/typelevel/spotted-leopards
Totally agree with @smarter on bin compatibility. If we wanted to get this in to cats 2.x, we'd have needed to do it prior to Scala 3 final release. I'd really like to see this included in the future though (perhaps Cats 3) along with built-in support for derivation (not via an add-on project).
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This Pull Request adds a implementation of the monad transformers
OptionT,IdT, andKleisli, for Scala 3. This new implementation uses the new feature of Scala 3, Opaque Types, which may allows us to have them implemented without overhead on the runtime memory.This may slightly improve performance for libraries that are based on these monad transformers, such as
http4s.