Scala 2.13.0 and Hash derivation rework #157
Conversation
| implicit def mkHashGenericProduct[A, R <: HList]( | ||
| implicit A: Generic.Aux[A, R], R: Lazy[HashBuilder[R]], ev: A <:< Product = null | ||
| ): MkHash[A] = instance( | ||
| x => R.value.hash(A.to(x), if (ev == null) MurmurHash3.productSeed else util.VersionSpecific.productSeed(x)), |
There was a problem hiding this comment.
I'm not sure about this to be honest.
There was a problem hiding this comment.
Could we use a pattern match here? like
x match {
case p : Product => util.VersionSpecific.productSeed(p)
case _ => MurmurHash3.productSeed
}There was a problem hiding this comment.
Yes, that's the part I'm not sure about. On one hand, ev: A <:< Product = null looks like a hack, but on the other pattern matching on the type parameter would break parametricity.
But what if the solution is to drop this law altogether from cats-testkit?
There was a problem hiding this comment.
I need to think about the law. Could we split this one method into two derivation methods with different priorities? One for Product another for the rest.
There was a problem hiding this comment.
Sure, that's also an option 👍
There was a problem hiding this comment.
Done. We can later remove the version specific code if we decide not to enforce this law.
|
This uncovered an issue with |
joroKr21
force-pushed
the
hash
branch
4 times, most recently
from
65c637b
to
2c9bbc4
Compare
Case classes' `hashCode` is not backwards compatible in Scala 2.13, because it mixes the `productPrefix` for better distribution. This means we need version specific code to pass the `Hash` laws. * Update dependencies for Scala 2.13.0 * Rework `Hash` derivation for consistency * Split product and coproduct derivation * Add a Scala version specific seed for `scala.Product` subtypes * Optimize `HashBuilder` to a one-pass hash * Replace usages of `Statics` (not recommended) with `MurmurHash3` * Test all variants of `Hash` derivation
joroKr21
changed the title
|
Updated to Scala 2.13.0 🎉 |
Case classes'
hashCodeis not backwards compatible in Scala 2.13,because it mixes the
productPrefixfor better distribution.This means we need version specific code to pass the
Hashlaws.Hashderivation for consistencyscala.ProductsubtypesHashBuilderto a one-pass hashStatics(not recommended) withMurmurHash3Hashderivation