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 have a idea for this usage:

//if I had a class like this
final class Test {
  def f = println("foo")
}
trait MyTrait {
  def doSomething = {
    println("boo")
  }
}
object MyTrait {
  implicit def innerObj(o:MixTest) = o.obj

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

you can use this trait as below:

import MyTrait._

val a = new Test
val b = a :: MyTrait
b.doSomething
b.f

for your example code:

val o = DBHelper.loadMyEntityFromDB(primaryKey) :: MyTrait
o.doSomething

I hope this can help you.

UPDATED

object AnyTrait {
  implicit def innerObj[T](o: MixTest[T]):T = o.obj

  def ::[T](o: T) = new MixTest(o)
  final class MixTest[T] private[AnyTrait](val obj: T) extends MyTrait
}

but this pattern has some restrict, you can't use some implicit helper method that defined already.

val a = new Test
a.f
val b = a :: AnyTrait
b.f1
b.f
val c = "say hello to %s" :: AnyTrait
println(c.intern)  // you can invoke String's method 
println(c.format("MyTrait"))  //WRONG. you can't invoke StringLike's method, though there defined a implicit method in Predef can transform String to StringLike, but implicit restrict one level transform, you can't transform MixTest to String then to StringLike.
c.f1
val d = 1 :: AnyTrait
println(d.toLong)
d.toHexString // WRONG, the same as above
d.f1