Scala 在不参考原始版本的情况下,为更高种类的类型召唤辅助设备
我正在尝试将Aux模式与更高种类的类型一起使用,直到之后才需要指定更高种类类型的参数。这类似于所描述的SO问题,但有一个显著的区别,我将从另一个方向,即从隐式def返回到auxScala 在不参考原始版本的情况下,为更高种类的类型召唤辅助设备,scala,generics,typeclass,type-level-computation,Scala,Generics,Typeclass,Type Level Computation,我正在尝试将Aux模式与更高种类的类型一起使用,直到之后才需要指定更高种类类型的参数。这类似于所描述的SO问题,但有一个显著的区别,我将从另一个方向,即从隐式def返回到aux // The are types that I want to convert to various things sealed trait ConversionType trait CaseA extends ConversionType object CaseA extends CaseA // In this ca
// The are types that I want to convert to various things
sealed trait ConversionType
trait CaseA extends ConversionType
object CaseA extends CaseA // In this case, convert to an optional
trait CaseB extends ConversionType
object CaseB extends CaseB // In this case, convert to a future etc...
trait Converter[Prefix] {
type Paramd[_]
def create[N](n:N): Paramd[N]
}
// Create the mechanism to convert from the cases, only doing case A for now...
object Converter {
type Aux[Prefix, Ret[_]] = Converter[Prefix] { type Paramd[_] = Ret[_] }
// *** Error happens here! ***
def apply[Prefix](implicit p:Converter[Prefix]): Aux[Prefix, p.Paramd] = p
implicit def makeOptionParamd: Aux[CaseA, Option] =
new Converter[CaseA] {
type Paramd[_] = Option[_]
override def create[N](n:N): Paramd[N] = Option[N](n)
}
}
// This seems to be fine...
val v = Converter.apply[CaseA].create("test")
我在上面提到的行中得到以下编译错误:
Error:(97, 78) type mismatch;
found : p.type (with underlying type Test.this.Converter[Prefix])
required: Test.Converter.Aux[Prefix,p.Paramd]
(which expands to) Test.this.Converter[Prefix]{type Paramd[_] = p.Paramd[_]}
def apply[Prefix](implicit p:Converter[Prefix]): Aux[Prefix, p.Paramd] = p
我做错了什么?你可能想要的是
object Converter {
type Aux[Prefix, Ret[_]] = Converter[Prefix] { type Paramd[A] = Ret[A] }
// compiles
def apply[Prefix](implicit p:Converter[Prefix]): Aux[Prefix, p.Paramd] = p
implicit def makeOptionParamd: Aux[CaseA, Option] =
new Converter[CaseA] {
type Paramd[A] = Option[A]
override def create[N](n:N): Paramd[N] = Option[N](n)
}
}
当你写作时
type Paramd[_] = Ret[_]
左右部分中的
是不相关的。这和
type Paramd[A] = Ret[_]
type Paramd[A] = Ret[B] forSome { type B }
因此,Aux[Prefix,p.Paramd]
与您的定义相当于Converter[Prefix]{type Paramd[A]=p.Paramd[\u]}
,并且p
没有此类型,因为p.Paramd[A]
不是p.Paramd[\u]