辅助模式在嵌套的隐式中无法正常工作

huangapple
go评论93阅读模式
英文:

Aux pattern not working for nested implicits

问题

以下是翻译好的代码部分：

  1. sealed trait Types
  3. object Types {
  4.   case class A(value: Int) extends Types
  6.   case class B(value: String, flag: Boolean) extends Types
  8.   case class L(value: Types, n: Int) extends Types
  9. }
  11. trait Generate[In] {
  12.   type Out
  14.   def generate(in: In): Out
  15. }
  17. object Generate {
  19.   type Aux[I, O] = Generate[I] {type Out = O}
  21.   implicit object AGenerate extends Generate[Types.A] {
  22.     override type Out = Int
  24.     override def generate(a: Types.A): Out = a.value
  25.   }
  27.   implicit object BGenerate extends Generate[Types.B] {
  28.     override type Out = String
  30.     override def generate(b: Types.B): Out = if (b.flag) b.value else "nope"
  31.   }
  33.   implicit def lGenerate[T, O](implicit aux: Aux[T, O]): Generate[Types.L] = new Generate[Types.L] {
  34.     override type Out = List[O]
  36.     override def generate(in: Types.L): Out = List.fill(in.n)(aux.generate(in.value))
  37.   }
  39.   implicit class RichGenerator[I](in: I) {
  40.     def generate[O](implicit aux: Aux[I, O]): O = aux.generate(in)
  41.   }
  42. }
  44. object Test extends App {
  45.   import Types._
  46.   import Generate._
  48.   val a = A(1)
  49.   val b = B("yep", flag = true)
  51.   println(a.generate) // 打印 1: Int
  52.   println(b.generate) // 打印 "yep": String
  54.   println(L(a, 3).generate) // 打印 List(1, 1, 1)
  55.   println(L(b, 2).generate) // 打印 List("yep", "yep")
  56.   println(L(L(a, 3), 2).generate) // 打印 List(List(1, 1, 1), List(1, 1, 1))
  57. }

请注意，我已经将 " 替换为实际的引号字符。如果你有其他问题，请随时提出。

英文:

I have the following Types

  1. sealed trait Types
  3. object Types {
  4.   case class A(value: Int) extends Types
  6.   case class B(value: String, flag: Boolean) extends Types
  8.   case class L(value: Types, n: Int) extends Types
  9. }

I want to have a generate method that will generate an output based on the input type, and the output might have different types. I tried to use the Aux pattern and for type A and type B the values are generated.

  1. trait Generate[In] {
  2.   type Out
  4.   def generate(in: In): Out
  5. }
  7. object Generate {
  9.   type Aux[I, O] = Generate[I] {type Out = O}
  11.   implicit object AGenerate extends Generate[Types.A] {
  12.     override type Out = Int
  14.     override def generate(a: Types.A): Out = a.value
  15.   }
  17.   implicit object BGenerate extends Generate[Types.B] {
  18.     override type Out = String
  20.     override def generate(b: Types.B): Out = if (b.flag) b.value else "nope"
  21.   }
  23. //  implicit def lGenerate[T, O](implicit aux: Aux[T, O]): Generate[Types.L] = new Generate[Types.L] {
  24. //    override type Out = List[O]
  25. //
  26. //    override def generate(in: Types.L): Out = List.fill(in.n)(aux.generate(in.value))
  27. //  }
  29.   implicit class RichGenerator[I](in: I) {
  30.     def generate[O](implicit aux: Aux[I, O]): O = aux.generate(in)
  31.   }
  32. }
  34. object Test extends App {
  35.   import Types._
  36.   import Generate._
  38.   val a = A(1)
  39.   val b = B("yep", flag = true)
  41.   println(a.generate) // prints 1: Int
  42.   println(b.generate) // prints "yep": String
  43. }

However, when I try to generate a value for type L, which depends on Types, then the implicit resolution fails.

My goal is to obtain the following outputs:

  1. println(L(a, 3).generate) \\ prints List(1,1,1)
  2. println(L(b, 2).generate) \\ prints List("yep", "yep")
  3. println(L(L(a,3), 2).generate) \\ prints List(List(1,1,1), List(1,1,1))

答案1

得分: 2

你可能想要正确地将 Aux 类型链接在一起。

首先，让我们将 L 做成泛型：

  1. final case class L[T <: Types](value: T, n: Int) extends Types

然后，让我们正确定义它的 Generator 实例：

  1. implicit def lGenerate[T <: Types, O](implicit aux: Aux[T, O]): Aux[Types.L[T], List[O]] =
  2.   new Generate[Types.L[T]] {
  3.     override type Out = List[O]
  4.   
  5.     override def generate(in: Types.L[T]): Out =
  6.       List.fill(in.n)(aux.generate(in.value))
  7.   }

你可以在 这里 看到代码运行的效果。

英文:

You probably want to properly link the Aux types together.

First, let's make L generic:

  1. final case class L[T &lt;: Types](value: T, n: Int) extends Types

Then, let's properly define its Generator instance:

  1. implicit def lGenerate[T &lt;: Types, O](implicit aux: Aux[T, O]): Aux[Types.L[T], List[O]] =
  2.   new Generate[Types.L[T]] {
  3.     override type Out = List[O]
  4.   
  5.     override def generate(in: Types.L[T]): Out =
  6.       List.fill(in.n)(aux.generate(in.value))
  7.   }

You can see the code running here.

huangapple
  • 本文由 发表于 2023年7月18日 04:18:20
  • 转载请务必保留本文链接：https://go.coder-hub.com/76707823.html
  • aux-pattern
  • functional-programming
  • scala
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