CODEWITHSUNDEEP
scalaself-type
mdenton8
mdenton8

Reputation: 616

Can I have multiple selftypes in Scala?

Can I have a class that can have two different self types in Scala? Or emulate it in some way?

object Hi {
    trait One {
        val num = 1
    }
    trait Two {
        val num = 2
    }
    class Test {
        this: One => {
            println(num)
        }
        this: Two => {
            println(num)
        }
    }
}

import Hi._
new Test with One
new Test with Two

Upvotes: 0

Views: 640

Answers (2)

Alexey Romanov
Alexey Romanov

Reputation: 170713

If you want to have multiple self-types simultaneously, you can write this: One with Two => .... Having two separate self-types, as in your example, just doesn't make much sense to me: if you have two different bodies (with different method implementations, different members, etc.) why not just make them into two separate classes/traits?

Upvotes: 3

som-snytt
som-snytt

Reputation: 39577

Subtyping:

scala> trait Num { def num: Int }
defined trait Num

scala> trait One extends Num { val num = 1 }
defined trait One

scala> trait Two extends Num { val num = 2 }
defined trait Two

scala> class Test { _: Num => def f() = println(num) }
defined class Test

scala> new Test with One
res0: Test with One = $anon$1@389adf1d

scala> .f()
1

Edit: Maybe that was a knee-jerk response and I should have said typeclasses.

Upvotes: 4

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