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scalatraitscompanion-object

Can a trait guarantee that it is inherited by a companion object at compile- or run-time

I have a trait for which the initialization is not inherently thread-safe, but is intended strictly for use as a base for companion objects, for which initialization is thread-safe by definition.

Is there some way to guarantee (either at compile- or run-time) that the trait is always extended by a companion object? The trait has a method that is always and only called during companion-object initialization, which could be the site of the verification.

Solution

  • If the trait must be extended by exactly 1 object, you can check it at compiletime like this:

    trait Foo { this: Bar.type =>
  ...
}

object Bar extends Foo

    If you need several objects to extend it, you could try something based on the Singleton magical type:

    trait Foo { this: Singleton =>
  ...
}

    but I don't know if that works.