Scala factory for generic types using the apply method?

Question

Suppose that I have the following trait that defines an interface and takes a couple of type parameters...

trait Foo[A, B] {

    // implementation details not i         


        

Answer 1

How about:

trait Foo[A, B]
trait Factory[A, B] {
  def make(thing: Thing): Foo[A, B]
}

class Thing

object Foo {
def apply[A, B](thing: Thing)(implicit ev: Factory[A, B]) = ev.make(thing)

private case class FooImpl[A, B](thing: Thing) extends Foo[A, B]
private case class AnotherFooImpl[A, B](thing: Thing) extends Foo[A, B]

implicit val fooImplFactory: Factory[Int, String] = new Factory[Int, String] {
  override def make(thing: Thing): Foo[Int, String] = new FooImpl[Int, String](thing)
}

implicit val anotherFooImplFactory: Factory[String, String] = new Factory[String, String] {
  override def make(thing: Thing): Foo[String, String] = new AnotherFooImpl[String, String](thing)
}

And now:

def main(args: Array[String]): Unit = {
  import Foo._

  val fooImpl = Foo[Int, String](new Thing)
  val anotherFooImpl = Foo[String, String](new Thing)

  println(fooImpl)
  println(anotherFooImpl)
}

Yields:

FooImpl(testing.X$Thing@4678c730)
AnotherFooImpl(testing.X$Thing@c038203)