类型别名结构类型是什么意思？

Question

I came across something like this recently

object example {
   type DButil = AnyRef {
     val a: Int
     def b: String
   }
}

Things that confused me is that usage of AnyRef here, later I dig a bit more, and I find you can also do this:

object apple {}
object example {
   type DButil = apple.type {
     val a: Int
     def b: String
   }
}

I've never seen this pattern before, any insights and comments are appreciated.

Answer 1

Type alias is just an additional name to the type. The constructions like AnyRef { val a: Int def b: String } apple.type { val a: Int def b: String } SomeSuperType { val structuralMember1: Int def structuralMember2: String }

is Anonymous Class/Type that inherits superclass behavior and contains additional structural type parts that defined in braces. And type alias is just a name for that Anonymous Type.