Implicits, pimpl pattern etc

Let's say that I have these classes:

case class A()
case class B()
case class C(a: A, b: B)

and these variables:

val a = A()
val b = B()

I开发者_C百科s there a way to get an instance of C implicitly and without making a and b implicit vals? I.e. if I have a method expecting a C:

def foo(c: C)

The case class A notation was deprecated. You have to use case class A(), otherwise assigning A to the val a will result in a referring to the companion object of the case class A which is generated behind the scene.

It's my understanding you wanted a to refer to the instance of the case class, not the companion object.

If so, what you're asking is possible - a and b don't have to be implicit, but you do have to add a new implicit method into the scope:

implicit def obtainC = new C(a, b)

Then, you have to put the implicit modifier to c in the method foo:

def foo(implicit c: C)

Complete session:

scala> case class A()
defined class A

scala> case class B()
defined class B

scala> case class C(a: A, b: B)
defined class C

scala> val a = A()
a: A = A()

scala> val b = B()
b: B = B()

scala> implicit def obtainC = new C(a, b)
obtainC: C

scala> def foo(implicit c: C) = {}
foo: (implicit c: C)Unit

scala> foo