Using this keyword to inherit?

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What is the difference between scala self-types and trait subclasses?

From example in scalatest site. There is one particular thing I don't really understand

trait FunSuiteStackBehaviors { 
                   this: FunSuite => //This line
                         def a() {}
                         def b() {}
}

class StackFunSuite extends FunSuite with FunSuiteStackBehaviors {}

As far as I understand, it seems like they try to assign some defs into a trait. But what does this: FunSuite => part do ? I tried to use extends FunSuite instead like

trait FunSuiteStackBehaviors extends FunSuite { 
                         def a() {}
                         def b() {}
}

class StackFunSuite extends FunSuite with FunSuiteStackBehaviors {}

and I still end up with same result. Are they the same thing ?

It's a self type. http://stackoverflow.com/questions/1990948/what-is-the-difference-between-scala-self-types-and-trait-subclasses http://stackoverflow.com/questions/tagged/self-type — retronym, Dec 03 '11 at 22:32
Hmm. those question doesn't come up when I try to search. Thanks for pointing that out. — Tg., Dec 03 '11 at 22:35

score 1 · Answer 1 · answered Dec 03 '11 at 22:40

1

the this: => XXXX is called a self type annotation http://www.scala-lang.org/node/124 Basically, you're specifying the type of "this" (current object) to the type specified. Kind of a "cast from the inside"

answered Dec 03 '11 at 22:40

GClaramunt

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score 0 · Answer 2 · answered Dec 03 '11 at 22:38

this: FunSuite => is called self type annotation. There is nothing special about "this" Both snippets are equivalent. Here is some discussion on its rationale. In short self type annotation helps to signify compositional nature rather than IS-A relation.

Using this keyword to inherit?

2 Answers2

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