案例类的应用方法类型(Case class's apply method type)

案例类的应用方法类型(Case class's apply method type)

我试图使用type字段，但似乎我做错了什么。 它似乎与经典类一起工作，但由于某种原因，案例类的apply类型不匹配。

object Common { type EntityId = Long } import Common._ abstract class IdStore { self => type Entity type Ref <: IdRef[_] type Self <: IdStore {type Entity = self.Entity; type Ref = self.Ref} def apply(data: Map[Ref, Entity]): Self def data: Map[Ref, Entity] def merge(other: Self): Self = apply(data ++ other.data) } trait IdRef[T] { def id: T } trait EntityIdRef extends IdRef[EntityId] {} class TestStore(val data: Map[IdRef[Int], Object]) extends IdStore { override type Entity = Object override type Ref = IdRef[Int] override type Self = TestStore override def apply(data: Map[Ref, Entity]): Self = new TestStore(data) } case class TestCaseClassStore(data: Map[IdRef[Int], Object]) extends IdStore { override type Entity = Object override type Ref = IdRef[Int] override type Self = TestCaseClassStore }

错误

Main.scala:34: error: class TestCaseClassStore needs to be abstract, since method apply in class IdStore of type (data: Map[TestCaseClassStore.this.Ref,TestCaseClassStore.this.Entity])TestCaseClassStore.this.Self is not defined case class TestCaseClassStore(data: Map[IdRef[Int], Object]) extends IdStore { ^ one error found

代码也在Ideone提供 。

I was trying to use type field, but it seems I did something wrong. It seems to be working with classic classes, but for some reason type of case class's apply doesn't match.

object Common { type EntityId = Long } import Common._ abstract class IdStore { self => type Entity type Ref <: IdRef[_] type Self <: IdStore {type Entity = self.Entity; type Ref = self.Ref} def apply(data: Map[Ref, Entity]): Self def data: Map[Ref, Entity] def merge(other: Self): Self = apply(data ++ other.data) } trait IdRef[T] { def id: T } trait EntityIdRef extends IdRef[EntityId] {} class TestStore(val data: Map[IdRef[Int], Object]) extends IdStore { override type Entity = Object override type Ref = IdRef[Int] override type Self = TestStore override def apply(data: Map[Ref, Entity]): Self = new TestStore(data) } case class TestCaseClassStore(data: Map[IdRef[Int], Object]) extends IdStore { override type Entity = Object override type Ref = IdRef[Int] override type Self = TestCaseClassStore }

Error

Main.scala:34: error: class TestCaseClassStore needs to be abstract, since method apply in class IdStore of type (data: Map[TestCaseClassStore.this.Ref,TestCaseClassStore.this.Entity])TestCaseClassStore.this.Self is not defined case class TestCaseClassStore(data: Map[IdRef[Int], Object]) extends IdStore { ^ one error found

Code is also available at Ideone.

最满意答案

我怀疑你有一个关于案例类错误的细节：

案例类没有免费应用功能！

它们带有一个伴随对象，该对象具有工厂apply函数来创建案例类的新实例。 那是：

case class Foo(bar: Int)

类似于

class Foo(val bar: Int) object Foo { def apply(bar: Int): Foo = new Foo(bar) }

所以，在你的代码中

case class TestCaseClassStore(data: Map[IdRef[Int], Object]) extends IdStore { override type Entity = Object override type Ref = IdRef[Int] override type Self = TestCaseClassStore }

缺少IdStore所需的apply函数。

考虑到这一点，您确定IdStore定义的apply函数是您想要的吗？

I suspect you got one detail about case classes wrong:

Case classes do not come with free apply functions!

They come with a companion object that has a factory apply function to create new instances of your case class. That is:

case class Foo(bar: Int)

is similar to

class Foo(val bar: Int) object Foo { def apply(bar: Int): Foo = new Foo(bar) }

So, in your code

case class TestCaseClassStore(data: Map[IdRef[Int], Object]) extends IdStore { override type Entity = Object override type Ref = IdRef[Int] override type Self = TestCaseClassStore }

is missing the apply function required in IdStore.

Considering this, are you sure that the apply function defined in IdStore is what you want?