How to mix-in a trait to instance?

Question

Given a trait MyTrait:

trait MyTrait {
  def doSomething = println(\"boo\")
}

it can be mixed into a class with extends<

Answer 1

I usually used a implicit to mix in a new method to an existing object.

See, if I have some code as below:

final class Test {
  def f = "Just a Test"
  ...some other method
}
trait MyTrait {
  def doSomething = {
    println("boo")
  }
}
object HelperObject {
  implicit def innerObj(o:MixTest) = o.obj

  def mixWith(o:Test) = new MixTest(o)
  final class MixTest private[HelperObject](obj:Test) extends MyTrait
}

and then you can use MyTrait method with an already existing object Test.

val a = new Test
import HelperObject._
val b = HelperObject.mixWith(a)
println(b.f)
b.doSomething

in your example, you can use like this:

import HelperObject._
val o = mixWith(DBHelper.loadMyEntityFromDB(primaryKey));
o.doSomething

I am thinking out a prefect syntax to define this HelperObject:

trait MyTrait {
  ..some method
}
object MyTrait {
  implicit def innerObj(o:MixTest) = o.obj

  def ::(o:Test) = new MixTest(o)
  final class MixTest private[MyTrait](obj:Test) extends MyTrait
}
//then you can use it
val a = new Test
val b = a :: MyTrait
b.doSomething
b.f
// for your example
val o = DBHelper.loadMyEntityFromDB(primaryKey) :: MyTrait
o.doSomething