在Scala中，有没有一种方法可以指定返回类型应该与方法调用者的类型匹配？

Question

For example, I have a class called Foo

abstract class Foo {
    def f(): ??? = { ... }
}
class Bar extends Foo {
    ...
}
class Baz extends Foo {
    ...
}

What I'd like is a way for f to return a Bar when it's called by Bar, and a Baz when it's called by Baz. Both Bar and Baz would have the same constructor, so the code in f would be the same both times, except for whether I have to say new Bar(...) or new Baz(...). Is there any way to say new TypeOfWhateverClassIsCallingMe(...)?

Answer 1

Sounds like you want F-Bounded types. You'll still have to implement it for all subclasses however, as the parent class has no knowledge of the child constructors (A "Mammal" does not know how to make a "Cat").

abstract class Foo[T <: Foo[T]] {
    def createMe(): T
}

class Bar extends Foo[Bar] {
    override def createMe() = new Bar
}

class Baz extends Foo[Baz] {
    override def createMe() = new Baz
}

This basically gives you compile-time safety, all children of Foo need to implement a method that creates something of its own class.

In-depth discussion here .

Answer 2

假设您要调用该方法的具体子类的类型（我不会将其称为“方法调用者的类型”，而是“被调用者的类型”），则可以执行

def f(): this.type = ???