Hash typeclass #1712
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,17 @@ | ||
| package cats | ||
| package instances | ||
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| import cats.functor._ | ||
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| trait HashInstances { | ||
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| implicit val catsContravariantForHash: Contravariant[Hash] = | ||
| new Contravariant[Hash] { | ||
| /** | ||
| * Derive a `Hash` for `B` given an `Hash[A]` and a function `B => A`. | ||
| */ | ||
| def contramap[A, B](ha: Hash[A])(f: B => A): Hash[B] = Hash.by(f)(ha) | ||
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There was a problem hiding this comment. A question: where should tests for instances of There was a problem hiding this comment. never mind, i've found it in |
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| } | ||
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| } | ||
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| Original file line number | Diff line number | Diff line change |
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| @@ -0,0 +1,18 @@ | ||
| package cats | ||
| package syntax | ||
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| import cats.macros.Ops | ||
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| trait HashSyntax { | ||
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| implicit def catsSyntaxHash[A: Hash](a: A): HashOps[A] = | ||
| new HashOps[A](a) | ||
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| } | ||
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| final class HashOps[A: Hash](a: A) { | ||
| /** | ||
| * Gets the hash code of this object given an implicit `Hash` instance. | ||
| */ | ||
| def hash: Int = macro Ops.unop0[Int] | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,58 @@ | ||
| package cats.kernel | ||
| package laws | ||
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| import org.typelevel.discipline._ | ||
| import org.scalacheck._ | ||
| import org.scalacheck.Prop._ | ||
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| import scala.util.hashing._ | ||
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| object HashLaws { | ||
| def apply[A : Eq : Arbitrary]: HashLaws[A] = | ||
| new HashLaws[A] { | ||
| def Equ = implicitly[Eq[A]] | ||
| def Arb = implicitly[Arbitrary[A]] | ||
| } | ||
| } | ||
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| /** | ||
| * @author Tongfei Chen | ||
| */ | ||
| trait HashLaws[A] extends Laws { | ||
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| implicit def Equ: Eq[A] | ||
| implicit def Arb: Arbitrary[A] | ||
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| def hash(implicit A: Hash[A]): HashProperties = new HashProperties( | ||
| name = "hash", | ||
| parent = None, | ||
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There was a problem hiding this comment. Shouldn't this have There was a problem hiding this comment. OrderLaws's parent is also None. But EqLaws are listed below in the There was a problem hiding this comment. seems like we should have There was a problem hiding this comment. I couldn't find |
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| Rules.serializable(Equ), | ||
| "compatibility-hash" -> forAll { (x: A, y: A) => | ||
| !(A.eqv(x, y)) ?|| (Hash.hash(x) == Hash.hash(y)) | ||
| } | ||
| ) | ||
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| def sameAsUniversalHash(implicit A: Hash[A]): HashProperties = new HashProperties( | ||
| name = "sameAsUniversalHash", | ||
| parent = None, | ||
| Rules.serializable(Equ), | ||
| "same-as-universal-hash" -> forAll { (x: A, y: A) => | ||
| (A.hash(x) == x.hashCode) && (Hash.fromUniversalHashCode[A].hash(x) == x.hashCode()) && | ||
| (A.eqv(x, y) == Hash.fromUniversalHashCode[A].eqv(x, y)) | ||
| } | ||
| ) | ||
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| def sameAsScalaHashing(implicit catsHash: Hash[A], scalaHashing: Hashing[A]): HashProperties = new HashProperties( | ||
| name = "sameAsScalaHashing", | ||
| parent = None, | ||
| Rules.serializable(Equ), | ||
| "same-as-scala-hashing" -> forAll { (x: A, y: A) => | ||
| (catsHash.hash(x) == Hash.fromHashing(scalaHashing).hash(x)) && | ||
| (catsHash.eqv(x, y) == Hash.fromHashing(scalaHashing).eqv(x, y)) | ||
| } | ||
| ) | ||
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| class HashProperties(name: String, parent: Option[RuleSet], props: (String, Prop)*) | ||
| extends DefaultRuleSet(name, parent, props: _*) | ||
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| } | ||
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I think this can be also
Cartesian[Hash]: you can hash each item then combine them in one of many ways. Maybe the fact that there are many ways to combine means it should not be implicit, but we can give functions that do so.There was a problem hiding this comment.
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Changed to
ContravariantCartesian. Thanks! I didn't know the existence ofCartesianbefore. I made it implicit: the standard way to combine items isscala.util.hashing.MurmurHash3.productHash.