強制性狀由一個對象實現

Question

如何強制scala中的特徵只能被對象（不是類，特徵等）擴展？

我有以下星座：

trait Outer { self: SomeOtherClass => 
    def member: Inner.type = Inner 

    /* some other methods... */ 

    trait Inner { iself => 
    def parent: self.type = self 
    /* other methods... */ 
    } 
} 

我的問題是：我怎麼能強制執行內部特質必須通過的對象來實現（如對象內延伸內{...}）？

我希望每個實現Outer的類都有一個內部對象，它攜帶一些狀態+從外部獲取內部的可能性，反之亦然。

最好的問候，

約亨

編輯：

例子：

// compiles 
class C extends Outer { 
    object Inner extends Inner { ... } 
} 

// doesn't compile 
class C extends Outer { 
    class Inner extends Inner { ... } 
} 

Answer 1

使用Singleton自我類型：

trait Outer { 
    def member: Inner 
    /* other methods... */ 
    trait Inner { self: Singleton => 
    def parent: Outer.this.type = Outer.this 
    /* other methods... */ 
    } 
} 

class OImpl extends Outer { 
    // Note that OImpl's subclasses can't override member this way 
    // You could also do private[this] object member0 extends Inner 
    // and override lazy val member = member0 to restore overridability 
    // The laziness of object and lazy val mean that member0 won't be created 
    // if a subclass doesn't use it. 
    override object member extends Inner { 
    // ... 
    } 
    // ... 
}