特征不符合类型参数边界

Question

我有类型的问题.在这种情况下,我有两个基本方法的特征,其中一个取决于另一个.之后,我有两个实现.你知道这里有什么问题吗？

编译器说:

type arguments [ImplDefinition,ImplDto,ImplDtoIdentifier] do not conform to trait ChildOperations's type parameter bounds [C <: Types.BaseT[A,I],A <: Types.IDObj[I],I <: IIdentifier]
[error] class ImplOperations extends Parent2(new ImplDefinition) with ChildOperations[ImplDefinition, ImplDto, ImplDtoIdentifier] {

代码:

/*
 * Generic Implementation
 */

object Types {

  type IDObj[I <: IIdentifier] = AnyRef {def id: I}

  type BaseT[A, I <: IIdentifier] = Parent1[A] {
    def id: Foo[I]
  }

}

trait IIdentifier extends Any {
  def id: Long

  override def toString = id.toString
}

class Parent1[A](a: String)

class Foo[A](a: String)

trait ChildDefinition[A <: Types.IDObj[I], I <: IIdentifier] {
  self: Parent1[A] =>

  def id(a: A): Foo[I]

}

class Parent2[A](a: A)

trait ChildOperations[C <: Types.BaseT[A, I], A <: Types.IDObj[I], I <: IIdentifier] {
  self: Parent2[C] =>

  def get(identifier: I): Option[A]
}

/*
 * Concrete Implementation
 */

case class ImplDtoIdentifier(id: Long) extends IIdentifier

case class ImplDto(id: ImplDtoIdentifier, name: String)

class ImplDefinition extends Parent1[ImplDto]("Value") with ChildDefinition[ImplDto, ImplDtoIdentifier] {
  override def id(a: ImplDto): Foo[ImplDtoIdentifier] = ???
}

class ImplOperations extends Parent2(new ImplDefinition) with ChildOperations[ImplDefinition, ImplDto, ImplDtoIdentifier] {
  self =>
  override def get(identifier: ImplDtoIdentifier): Option[ImplDto] = ??? // here I will use the id method from ImplDefinition
}

Answer 1

问题似乎是iddef 中的签名ImplDefinition。 Types.BaseT要求 adef id: Foo[I]但ImplDefinition只提供 adef id(a: ImplDto): Foo[ImplDtoIdentifier] 如果你将 a 添加到类def id:Foo[ImplDtoIdentifier] = ???中ImplDefinition，事情就会编译：

class ImplDefinition extends Parent1[ImplDto]("Value") with ChildDefinition[ImplDto, ImplDtoIdentifier] {
  def id:Foo[ImplDtoIdentifier] = ???
  override def id(a: ImplDto): Foo[ImplDtoIdentifier] = ???
}