self 类型注释中 this 和 self 的区别? [英] Difference between this and self in self-type annotations?

问题描述

在各种 Scala 文献中，我看到一些使用this"和其他使用self"的自我类型注释:

In various Scala literature I see some self-type annotations using "this" and others using "self":

trait A { this: B => ... }
trait A { self: B => ... }

使用this"或self"之间有什么真正的区别吗?你用什么名字有关系吗?这同样有效吗?

Is there any real difference between using "this" or "self"? Does it matter at all what name you use? Is this just as valid?

trait A { foo: B => ... }

推荐答案

这三种形式都是有效的，并且具有 B 被假定为 this 的类型的效果在 A 类中.

All three forms are valid, and have the effect that B is assumed as the type of this in class A.

前两个变体

trait A { self: B => ... }
trait A { foo: B => ... }

在特征A中引入self(分别为foo)作为this的别名.这对于从内部类访问 this 引用很有用.IE.然后，当从类访问特征 A 的 this 引用时，您可以使用 self 而不是 A.this嵌套在其中.示例:

introduce self (respectively, foo) as an alias for this in trait A. This is useful for accessing the this reference from an inner class. I.e. you could then use self instead of A.this when accessing the this reference of the trait A from a class nested within it. Example:

class MyFrame extends JFrame { frame =>    
  getContentPane().add( new JButton( "Hide" ) {
    addActionListener( new ActionListener {
      def actionPerformed( e: ActionEvent ) {
        // this.setVisible( false ) --> shadowed by JButton!
        frame.setVisible( false )
      }
    })
  })
}

第三个变体，

trait A { this: B => ... }

不为this引入别名；它只是设置 self 类型.

does not introduce an alias for this; it just sets the self type.

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