阿罗哈! :)
可以请有人指点我有用的scala / cats教程吗?在过去的几天里,我正努力让课程成为一个仿函数,我即将在我的显示器上打一个洞。我到目前为止找到的所有文档对我来说都没有帮助。
也许我应该试试Eta ...... = D.
这是我想成为仿函数的课程。除了“表演”之外,我的表现并不像我预期的那样。
package org.hudelundpfusch.utilites.decisions.data
import cats.{Functor, Show}
import cats.kernel.Eq
import cats.syntax.functor._
import cats.syntax.show._
import scala.reflect.runtime.universe
import scala.reflect.runtime.universe._
case class Fact[T <: Any] (name: String, value: T) (implicit private val paramTypeTagT: WeakTypeTag[T])
extends Equals {
val paramType: universe.Type = paramTypeTagT.tpe
val paramTypeClass: Option[Class[_ <: T]] = if (value != null) {
Some(value.getClass)
} else {
None
}
def map[A, B](fa: Fact[A])(f: A => B): Fact[B] = Fact[B](fa.name, f(fa.value))
override def canEqual(other: Any): Boolean = other.isInstanceOf[Fact[_]]
override def equals(other: Any): Boolean = other match {
case that: Fact[_] =>
(that canEqual this) &&
name == that.name
paramType == that.paramType &&
paramTypeClass == that.paramTypeClass &&
value == that.value
case _ => false
}
override def hashCode(): Int = {
val state = Seq(name, paramType, paramTypeClass, value)
state.map(_.hashCode()).foldLeft(0)((a, b) => 31 * a + b)
}
override def toString = s"Fact(name=${name}, paramType=$paramType, paramTypeClass=$paramTypeClass, value=$value)"
}
case object Fact extends Show[Fact[_]] {
override def show(t: Fact[_]): String = t.toString
}
提前致谢
祝你今天愉快
亚历克斯
更新:
package org.hudelundpfusch.utilites.decisions.data
import cats.{Functor, Show}
import cats.kernel.Eq
import cats.syntax.functor._
import cats.syntax.show._
import scala.reflect.runtime.universe
import scala.reflect.runtime.universe._
case class Fact[T <: Any] (name: String, value: T) (implicit private val paramTypeTagT: WeakTypeTag[T])
extends Functor[Fact]
with Equals {
val paramType: universe.Type = paramTypeTagT.tpe
val paramTypeClass: Option[Class[_ <: T]] = if (value != null) {
Some(value.getClass)
} else {
None
}
def map[A, B](fa: Fact[A])(f: A => B): Fact[B] = Fact[B](fa.name, f(fa.value))
override def canEqual(other: Any): Boolean = other.isInstanceOf[Fact[_]]
override def equals(other: Any): Boolean = other match {
case that: Fact[_] =>
(that canEqual this) &&
name == that.name
paramType == that.paramType &&
paramTypeClass == that.paramTypeClass &&
value == that.value
case _ => false
}
override def hashCode(): Int = {
val state = Seq(name, paramType, paramTypeClass, value)
state.map(_.hashCode()).foldLeft(0)((a, b) => 31 * a + b)
}
override def toString = s"Fact(name=${name}, paramType=$paramType, paramTypeClass=$paramTypeClass, value=$value)"
}
好的,我现在试过了:
object Fact {
implicit val factFunctor: Functor[Fact] = new Functor[Fact] {
override def map[A, B](fa: Fact[A])(f: A => B): Fact[B] = Fact[B](fa.name, f(fa.value))
}
implicit def factShow[T]: Show[Fact[T]] = new Show[Fact[T]] {
override def show(t: Fact[T]): String = this.toString
}
}
不幸的是,对映射函数的调用看起来有点麻烦:
package org.hudelundpfusch.utilites.decisions.data
object Fuddel {
def main(args: Array[String]): Unit = {
val fact1: Fact[Int] = Fact("Fact-1", 23)
val fact2 = Fact.factFunctor.map(fact1){x: Int => x * 2}
println(s"$fact2")
}
}
使用Cats,您不会扩展Show,Functor特征(OOP方式),您可以创建Show,Functor(FP方式)的隐式实例。
http://eed3si9n.com/herding-cats/Functor.html
https://typelevel.org/cats/typeclasses/functor.html
implicit def factShow[T]: Show[Fact[T]] = new Show[Fact[T]] {
override def show(t: Fact[T]): String = ???
}
// implicit object factFunctor extends Functor[Fact] {
// override def map[A, B](fa: Fact[A])(f: A => B): Fact[B] = ???
// }
implicit val factFunctor: Functor[Fact] = new Functor[Fact] {
override def map[A, B](fa: Fact[A])(f: A => B): Fact[B] = ???
}
Show[Fact[Int]].show(Fact("a", 1))
Functor[Fact].map(Fact("a", 1))(_ + 1)
import cats.syntax.show._
Fact("a", 1).show
import cats.syntax.functor._
Fact("a", 1).map(_ + 1)
以防万一,你的Fact[_]
中的case object Fact extends Show[Fact[_]]
是存在类型,而我的Fact
中的implicit object factFunctor extends Functor[Fact]
是更高级的类型。