"`class declaration head` {val_name:Type =>`class body`}"的语法含义是什么？

Question

在阅读有关Scala的一些文章时,我发现了一些带有好奇语法的例子,我可能会错误地理解它

class Child[C <: Child[C]] {
  some_name : C =>                   // here, what does it mean?
   var roomie : Option[C] = None

   def roomWith(aChild : C)= { 
     roomie = Some(aChild)
     aChild.roomie = Some(this) 
   }
}
class Boy extends Child[Boy]

我找到了类似特征的例子.

这是否意味着我this在类范围内声明对象的类型C？

Answer 1

它是一种自我类型的注释.

这意味着类Child必须是类型C,即创建必须满足给定类的继承依赖项.

一个小例子:

scala> trait Baz
defined trait Baz


scala> class Foo {
     | self:Baz => 
     | }
defined class Foo


scala> val a = new Foo
<console>:9: error: class Foo cannot be instantiated because it does not conform to its self-type Foo with Baz
       val a = new Foo
               ^

scala> val a = new Foo with Baz
a: Foo with Baz = $anon$1@199de181


scala> class Bar extends Foo with Baz
defined class Bar

在这种情况下Foo也需要是一个Baz.满足该要求,Foo可以创建一个实例.此外,定义一个新类(在这种情况下Bar)也有它的要求Baz.

见:http: //www.scala-lang.org/node/124