在Scala中使用newtype时需要定义函数吗？

问题描述 投票：1回答：2

我正在尝试更多地了解类型，并使用它们来避免愚蠢的错误。

我问了一个类似的问题here，但是遇到了与我在此处显示的问题类似的问题（我认为），最终放弃了答案。对这个问题的评论建议我调查newtype。

表面上看似简单，但我仍然挠头。

我有此代码：

  package com.craigtreptow.scrayz
  import io.estatico.newtype.macros.newtype

    package object Colors {

    def multiply(c: Color, n: Double): Color = {
      Color(
        c.red   * n,
        c.green * n,
        c.blue  * n
       )
    }

    @newtype case class Red(toDouble: Double)
    case class Color(red: Red, green: Double, blue: Double)
}

以上产生这些错误：

[info] Compiling 1 Scala source to /Users/Ctreptow/code/scrayz/target/scala-2.13/classes ...
[error] /Users/Ctreptow/code/scrayz/src/main/scala/com/craigtreptow/scrayz/Colors/package.scala:11:15: value * is not a member of com.craigtreptow.scrayz.Colors.package.Red
[error]       c.red   * n,
[error]               ^
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 4 s, completed Apr 30, 2020 3:19:36 PM

我认为我应该能够自动派生*，因为这种新类型最终是Double。

我可以吗？如果没有，如何用参数定义自己的函数？例如*

scala user-defined-types newtype
2个回答
0
投票

我认为您正在寻找这样的东西：

def multiply(color: Color, n: Double): Color = {
    Color(
      color.red * n,
      color.green * n,
      color.blue * n
    )
  }

  case class Red(toDouble: Double) {
    def *(n: Double): Red = Red(n * this.toDouble)
  }

  case class Green(toDouble: Double) {
    def *(n: Double): Green = Green(n * this.toDouble)
  }

  case class Blue(toDouble: Double) {
    def *(n: Double): Blue = Blue(n * this.toDouble)
  }

  case class Color(red: Red, green: Green, blue: Blue)

  print(multiply(Color(Red(4), Green(3), Blue(2)), 3))
0
投票

您可以手动定义*

@newtype case class Red(toDouble: Double) {
  def *(n: Double): Red = Red(toDouble * n)
}

如果要自动派生所有方法（使用Double的相应方法，则可以定义一个宏注释@exportMethods

import scala.annotation.{StaticAnnotation, compileTimeOnly}
import scala.language.experimental.macros
import scala.reflect.macros.blackbox

@compileTimeOnly("enable macro paradise")
class exportMethods extends StaticAnnotation {
  def macroTransform(annottees: Any*): Any = macro ExportMethodsMacro.impl
}

object ExportMethodsMacro {
  def impl(c: blackbox.Context)(annottees: c.Tree*): c.Tree = {
    import c.universe._
    annottees match {
      case q"$mods class $tpname[..$tparams] $ctorMods(...$paramss) extends { ..$earlydefns } with ..$parents { $self => ..$stats }" :: tail =>
        val exportedMethods = paramss match {
          case (q"$_ val $paramName: $paramType = $_" :: Nil) :: Nil =>
            val paramTyp = c.typecheck(tq"$paramType", mode = c.TYPEmode).tpe
            paramTyp.decls.map(_.asMethod)
              .filterNot(s => Set(paramName, TermName("getClass"), TermName("<init>")).contains(s.name))
              .map(s => {
                val paramss1 = s.paramLists.map(_.map(s => q"val ${s.name.toTermName}: ${s.typeSignature}"))
                val paramss2 = s.paramLists.map(_.map(s => q"${s.name.toTermName}"))
                if (s.returnType =:= paramTyp)
                  q"def ${s.name}(...$paramss1): $tpname = ${tpname.toTermName}.apply($paramName.${s.name}(...$paramss2))"
                else
                  q"def ${s.name}(...$paramss1): ${s.returnType} = $paramName.${s.name}(...$paramss2)"
              })
          case _ => c.abort(c.enclosingPosition, "class must have single parameter")
        }
        q"""
          $mods class $tpname[..$tparams] $ctorMods(...$paramss) extends { ..$earlydefns } with ..$parents { $self =>
            ..$stats
            ..$exportedMethods
          }
          ..$tail
        """
    }
  }
}

用法：

import io.estatico.newtype.macros.newtype

@exportMethods @newtype case class Red(toDouble: Double)

//Warning:scalac: {
//  type Red = Red.Type;
//  object Red extends scala.AnyRef {
//    def <init>() = {
//      super.<init>();
//      ()
//    };
//    def apply(toDouble: Double): Red = toDouble.asInstanceOf[Red];
//    final implicit class Ops$newtype extends AnyVal {
//      <paramaccessor> val $this$: Type = _;
//      def <init>($this$: Type) = {
//        super.<init>();
//        ()
//      };
//      def toDouble: Double = $this$.asInstanceOf[Double];
//      def toByte: Byte = toDouble.toByte;
//      def toShort: Short = toDouble.toShort;
//      def toChar: Char = toDouble.toChar;
//      def toInt: Int = toDouble.toInt;
//      def toLong: Long = toDouble.toLong;
//      def toFloat: Float = toDouble.toFloat;
//      def unary_$plus: Red = Red.apply(toDouble.unary_$plus);
//      def unary_$minus: Red = Red.apply(toDouble.unary_$minus);
//      def $plus(x: String): String = toDouble.$plus(x);
//      def $eq$eq(x: Byte): Boolean = toDouble.$eq$eq(x);
//      def $eq$eq(x: Short): Boolean = toDouble.$eq$eq(x);
//      def $eq$eq(x: Char): Boolean = toDouble.$eq$eq(x);
//      def $eq$eq(x: Int): Boolean = toDouble.$eq$eq(x);
//      def $eq$eq(x: Long): Boolean = toDouble.$eq$eq(x);
//      def $eq$eq(x: Float): Boolean = toDouble.$eq$eq(x);
//      def $eq$eq(x: Double): Boolean = toDouble.$eq$eq(x);
//      def $bang$eq(x: Byte): Boolean = toDouble.$bang$eq(x);
//      def $bang$eq(x: Short): Boolean = toDouble.$bang$eq(x);
//      def $bang$eq(x: Char): Boolean = toDouble.$bang$eq(x);
//      def $bang$eq(x: Int): Boolean = toDouble.$bang$eq(x);
//      def $bang$eq(x: Long): Boolean = toDouble.$bang$eq(x);
//      def $bang$eq(x: Float): Boolean = toDouble.$bang$eq(x);
//      def $bang$eq(x: Double): Boolean = toDouble.$bang$eq(x);
//      def $less(x: Byte): Boolean = toDouble.$less(x);
//      def $less(x: Short): Boolean = toDouble.$less(x);
//      def $less(x: Char): Boolean = toDouble.$less(x);
//      def $less(x: Int): Boolean = toDouble.$less(x);
//      def $less(x: Long): Boolean = toDouble.$less(x);
//      def $less(x: Float): Boolean = toDouble.$less(x);
//      def $less(x: Double): Boolean = toDouble.$less(x);
//      def $less$eq(x: Byte): Boolean = toDouble.$less$eq(x);
//      def $less$eq(x: Short): Boolean = toDouble.$less$eq(x);
//      def $less$eq(x: Char): Boolean = toDouble.$less$eq(x);
//      def $less$eq(x: Int): Boolean = toDouble.$less$eq(x);
//      def $less$eq(x: Long): Boolean = toDouble.$less$eq(x);
//      def $less$eq(x: Float): Boolean = toDouble.$less$eq(x);
//      def $less$eq(x: Double): Boolean = toDouble.$less$eq(x);
//      def $greater(x: Byte): Boolean = toDouble.$greater(x);
//      def $greater(x: Short): Boolean = toDouble.$greater(x);
//      def $greater(x: Char): Boolean = toDouble.$greater(x);
//      def $greater(x: Int): Boolean = toDouble.$greater(x);
//      def $greater(x: Long): Boolean = toDouble.$greater(x);
//      def $greater(x: Float): Boolean = toDouble.$greater(x);
//      def $greater(x: Double): Boolean = toDouble.$greater(x);
//      def $greater$eq(x: Byte): Boolean = toDouble.$greater$eq(x);
//      def $greater$eq(x: Short): Boolean = toDouble.$greater$eq(x);
//      def $greater$eq(x: Char): Boolean = toDouble.$greater$eq(x);
//      def $greater$eq(x: Int): Boolean = toDouble.$greater$eq(x);
//      def $greater$eq(x: Long): Boolean = toDouble.$greater$eq(x);
//      def $greater$eq(x: Float): Boolean = toDouble.$greater$eq(x);
//      def $greater$eq(x: Double): Boolean = toDouble.$greater$eq(x);
//      def $plus(x: Byte): Red = Red.apply(toDouble.$plus(x));
//      def $plus(x: Short): Red = Red.apply(toDouble.$plus(x));
//      def $plus(x: Char): Red = Red.apply(toDouble.$plus(x));
//      def $plus(x: Int): Red = Red.apply(toDouble.$plus(x));
//      def $plus(x: Long): Red = Red.apply(toDouble.$plus(x));
//      def $plus(x: Float): Red = Red.apply(toDouble.$plus(x));
//      def $plus(x: Double): Red = Red.apply(toDouble.$plus(x));
//      def $minus(x: Byte): Red = Red.apply(toDouble.$minus(x));
//      def $minus(x: Short): Red = Red.apply(toDouble.$minus(x));
//      def $minus(x: Char): Red = Red.apply(toDouble.$minus(x));
//      def $minus(x: Int): Red = Red.apply(toDouble.$minus(x));
//      def $minus(x: Long): Red = Red.apply(toDouble.$minus(x));
//      def $minus(x: Float): Red = Red.apply(toDouble.$minus(x));
//      def $minus(x: Double): Red = Red.apply(toDouble.$minus(x));
//      def $times(x: Byte): Red = Red.apply(toDouble.$times(x));
//      def $times(x: Short): Red = Red.apply(toDouble.$times(x));
//      def $times(x: Char): Red = Red.apply(toDouble.$times(x));
//      def $times(x: Int): Red = Red.apply(toDouble.$times(x));
//      def $times(x: Long): Red = Red.apply(toDouble.$times(x));
//      def $times(x: Float): Red = Red.apply(toDouble.$times(x));
//      def $times(x: Double): Red = Red.apply(toDouble.$times(x));
//      def $div(x: Byte): Red = Red.apply(toDouble.$div(x));
//      def $div(x: Short): Red = Red.apply(toDouble.$div(x));
//      def $div(x: Char): Red = Red.apply(toDouble.$div(x));
//      def $div(x: Int): Red = Red.apply(toDouble.$div(x));
//      def $div(x: Long): Red = Red.apply(toDouble.$div(x));
//      def $div(x: Float): Red = Red.apply(toDouble.$div(x));
//      def $div(x: Double): Red = Red.apply(toDouble.$div(x));
//      def $percent(x: Byte): Red = Red.apply(toDouble.$percent(x));
//      def $percent(x: Short): Red = Red.apply(toDouble.$percent(x));
//      def $percent(x: Char): Red = Red.apply(toDouble.$percent(x));
//      def $percent(x: Int): Red = Red.apply(toDouble.$percent(x));
//      def $percent(x: Long): Red = Red.apply(toDouble.$percent(x));
//      def $percent(x: Float): Red = Red.apply(toDouble.$percent(x));
//      def $percent(x: Double): Red = Red.apply(toDouble.$percent(x))
//    };
//    implicit def opsThis(x: Ops$newtype): Type = x.$this$;
//    @new _root_.scala.inline() implicit def unsafeWrap: Coercible[Repr, Type] = Coercible.instance;
//    @new _root_.scala.inline() implicit def unsafeUnwrap: Coercible[Type, Repr] = Coercible.instance;
//    @new _root_.scala.inline() implicit def unsafeWrapM[M[_]]: Coercible[M[Repr], M[Type]] = Coercible.instance;
//    @new _root_.scala.inline() implicit def unsafeUnwrapM[M[_]]: Coercible[M[Type], M[Repr]] = Coercible.instance;
//    @new _root_.scala.inline() implicit def cannotWrapArrayAmbiguous1: Coercible[_root_.scala.Array[Repr], _root_.scala.Array[Type]] = Coercible.instance;
//    @new _root_.scala.inline() implicit def cannotWrapArrayAmbiguous2: Coercible[_root_.scala.Array[Repr], _root_.scala.Array[Type]] = Coercible.instance;
//    @new _root_.scala.inline() implicit def cannotUnwrapArrayAmbiguous1: Coercible[_root_.scala.Array[Type], _root_.scala.Array[Repr]] = Coercible.instance;
//    @new _root_.scala.inline() implicit def cannotUnwrapArrayAmbiguous2: Coercible[_root_.scala.Array[Type], _root_.scala.Array[Repr]] = Coercible.instance;
//    def deriving[TC[_]](implicit ev: TC[Repr]): TC[Type] = ev.asInstanceOf[TC[Type]];
//    type Repr = Double;
//    type Base = _root_.scala.Any {
//      type __Red__newtype
//    };
//    abstract trait Tag extends _root_.scala.Any;
//    type Type <: Base with Tag
//  };
//  ()
//}

multiply(Color(Red(1.0), 2.0, 3.0), 4.0) //Color(4.0,8.0,12.0)

注释的顺序很重要（首先扩展@exportMethods，其次扩展@newtype）。

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