Why do implicits which are defined in a separate trait after the usage result in a compile error?

Question

Why does the following code results into a compile error:

class MyImplicit

class FooTest extends ImplicitProvider {

  def getImplicit(implicit i: MyImplicit) = i

  getImplicit
}

trait ImplicitProvider {
  implicit val myImplicit = new MyImplicit
}

The compile error is:

could not find implicit value for parameter i: MyImplicit getImplicit

If I move the trait ImplicitProvider above the class FooTest everything works fine.

I compile with scala 2.11.7 and sbt 0.13.9.

Is this expected behaviour or a bug?

Answer 1

This appears to be a "feature". Take a look at the comments in this ticket.

Apparently this is expected behaviour when the type of the implicit is not explicitly specified. So you can fix it by adding a type annotation to the implicit val.

class MyImplicit

class FooTest extends ImplicitProvider {

  def getImplicit(implicit i: MyImplicit) = i

  getImplicit
}

trait ImplicitProvider {
  implicit val myImplicit: MyImplicit = new MyImplicit
}