Scala 超过2种类型的无形状类型析取
如何为shapeless中的3个或更多类型提供类型析取?例如:Scala 超过2种类型的无形状类型析取,scala,shapeless,type-safety,Scala,Shapeless,Type Safety,如何为shapeless中的3个或更多类型提供类型析取?例如: import shapeless._ object Tst extends App { sealed trait Base final case class A() extends Base final case class B() extends Base final case class C() extends Base final case class D() extends Base def
import shapeless._
object Tst extends App {
sealed trait Base
final case class A() extends Base
final case class B() extends Base
final case class C() extends Base
final case class D() extends Base
def AorB[T: (A |∨| B)#λ](t: T): Unit =
t match {
case _: A => println("A")
case _: B => println("B")
}
AorB(A()) //Ok
AorB(B()) //Ok
def AorBorC[T: (A |∨| B |∨| C)#λ](t: T): Unit =
t match {
case _: A => println("A")
case _: B => println("B")
case _: C => println("C")
}
AorBorC(A()) //compile-error
AorBorC(B()) //compile-error
AorBorC(C()) //Ok
}
从两种类型的析取可以看出,它工作得非常好。但对于3种类型的析取,它并不像预期的那样工作
编译错误包括:
Error:(28, 10) Cannot prove that (Tst.A => Nothing) => Nothing <:< Object{type λ[X] = (X => Nothing) => Nothing <:< Tst.A => Nothing with Tst.B => Nothing => Nothing} => Nothing with Tst.C => Nothing => Nothing.
AorBorC(A())
Error:(28,10)无法证明(Tst.A=>Nothing=>Nothing=>Nothing=>Tst.B=>Nothing=>Nothing}=>Nothing=>Tst.C=>Nothing=>Nothing。
AorBorC(A())
及
Error:(29,10)无法证明(Tst.B=>Nothing=>Nothing)=>Nothing-Nothing-with-Tst.B=>Nothing=>Nothing}=>Nothing-with-Tst.C=>Nothing=>Nothing。
AorBorC(B())
不成形|∨|代码>不适用于超过2种类型
对于2种以上的类型,编码变得更加复杂
一种编码是2,4,8。。。类型
type ¬¬¬¬[T] = ¬¬[¬¬[T]]
type |∨∨|[T, U] = {
type λ[X] = ¬¬¬¬[X] <:< (T ∨ U)
}
def AorBorC[T: ((A ∨ B) |∨∨| (C ∨ C))#λ](t: T): Unit =
t match {
case _: A => println("A")
case _: B => println("B")
case _: C => println("C")
}
AorBorC(A()) //Ok
AorBorC(B()) //Ok
AorBorC(C()) //Ok
类型[T]=[T]]
类型|∨∨|[T,U]={
类型λ[X]=,,,,,[X]println(“A”)
案例:B=>println(“B”)
案例:C=>println(“C”)
}
AorBorC(A())//好的
AorBorC(B())//好的
AorBorC(C())//好的
另一种是针对任意数量的类型
trait Disj[T] {
type or[S] = Disj[T with ¬[S]]
type apply = ¬[T]
}
type ∨∨∨[T1, T2, T3] = Disj[¬[T1]]#or[T2]#or[T3]#apply
type |∨∨∨|[T1, T2, T3] = {
type λ[X] = ¬¬[X] <:< ∨∨∨[T1, T2, T3]
}
def AorBorC[T: |∨∨∨|[A, B, C]#λ](t: T): Unit =
t match {
case _: A => println("A")
case _: B => println("B")
case _: C => println("C")
}
AorBorC(A()) //Ok
AorBorC(B()) //Ok
AorBorC(C()) //Ok
trait Disj[T]{
类型或[S]=Disj[T,带[S]]
类型apply=,[T]
}
类型∨∨∨[T1,T2,T3]=Disj[,[T1]#或[T2]#或[T3]#适用
类型|∨∨∨|[T1、T2、T3]={
类型λ[X]=,,,[X]println(“A”)
案例:B=>println(“B”)
案例:C=>println(“C”)
}
AorBorC(A())//好的
AorBorC(B())//好的
AorBorC(C())//好的
trait Disj[T] {
type or[S] = Disj[T with ¬[S]]
type apply = ¬[T]
}
type ∨∨∨[T1, T2, T3] = Disj[¬[T1]]#or[T2]#or[T3]#apply
type |∨∨∨|[T1, T2, T3] = {
type λ[X] = ¬¬[X] <:< ∨∨∨[T1, T2, T3]
}
def AorBorC[T: |∨∨∨|[A, B, C]#λ](t: T): Unit =
t match {
case _: A => println("A")
case _: B => println("B")
case _: C => println("C")
}
AorBorC(A()) //Ok
AorBorC(B()) //Ok
AorBorC(C()) //Ok