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hash.scala
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hash.scala
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/*
* Copyright (c) 2015 Typelevel
*
* Permission is hereby granted, free of charge, to any person obtaining a copy of
* this software and associated documentation files (the "Software"), to deal in
* the Software without restriction, including without limitation the rights to
* use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
* the Software, and to permit persons to whom the Software is furnished to do so,
* subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
* FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
* COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
* IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
* CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
*/
package cats
package instances
import scala.annotation.tailrec
trait HashInstances extends kernel.instances.HashInstances {
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)
}
implicit def catsDeferForHash: Defer[Hash] = HashInstances.catsDeferForHashCache
}
object HashInstances {
private val catsDeferForHashCache: Defer[Hash] =
new Defer[Hash] {
case class Deferred[A](fa: () => Hash[A]) extends Hash[A] {
private lazy val resolve: Hash[A] = {
@tailrec
def loop(f: () => Hash[A]): Hash[A] =
f() match {
case Deferred(f) => loop(f)
case next => next
}
loop(fa)
}
override def hash(x: A): Int = resolve.hash(x)
/**
* Returns `true` if `x` and `y` are equivalent, `false` otherwise.
*/
override def eqv(x: A, y: A): Boolean = resolve.eqv(x, y)
}
override def defer[A](fa: => Hash[A]): Hash[A] = {
lazy val cachedFa = fa
Deferred(() => cachedFa)
}
}
}