Question

我将如何转换：

trait Foo[A <: Foo[A]]

到类型成员？

即，我想要的内容如下：

trait Foo {
  type A <: Foo {type A = ???}
}

但我遇到了困难，因为名称A已经在类型细化中被采用。这个问题类似（并衍生自）：F-bounded quantification through type member instead of type parameter?

Answer 1

使用自我类型：

scala> trait Foo { self => type A <: Foo {type A = self.A}}
defined trait Foo

scala> class Bar extends Foo { type A = Bar }
defined class Bar

scala> class Bar extends Foo { type A = Int }
<console>:10: error: overriding type A in trait Foo with bounds <: Foo{type A = Bar.this.A};
 type A has incompatible type
       class Bar extends Foo { type A = Int }
                                    ^

Scala将递归有界类型参数（F-bounded）转换为类型成员

1 个答案: