Implicits Abiguous and Override

implicts.scala

import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent._
import scala.concurrent.duration._

import scalaz._
import Scalaz._


object console extends App {

  object ambiguous {  
    
    object Foo {
      implicit val s: String = "foo"
    }

    object Bar {
      implicit val st: String = "bar" 
    }

    def printS(implicit string: String) = println(s"s: ${string}") 
    
    import Foo._
    import Bar._    

    // printS

    // [error] /home/luigi/workspace/test-scalaz-shapeless/src/main/scala/console.scala:26: ambiguous implicit values:
    // [error]  both value s in object Foo of type => String
    // [error]  and value st in object Bar of type => String
    // [error]  match expected type String

  }
  
  object implicitOverrride {
    // this work because Bar extends Foo

    trait Foo {
      implicit val s: String = "foo"
    }

    object Bar extends Foo {
      implicit val st: String = "bar" 
    }

    val foo: Foo = new Foo {}

    def printS(implicit string: String) = println(s"s: ${string}") 
    
    import foo._
    import Bar._  

    printS // s: bar
  }

  implicitOverrride

  object hiddenByName {  
    
    object Foo {
      implicit val s: String = "foo"
    }

    object Bar {
      val s: Int = 2 
    }

    def printS(implicit string: String) = println(s"s: ${string}") 

    import Foo._
    import Bar._    
    
    // printS
    // [error] /home/luigi/workspace/test-scalaz-shapeless/src/main/scala/console.scala:72: 
    // could not find implicit value for parameter string: String

  }

  // This is important!!
  object hiddenByName2 { 

    object Foo {
      implicit val s: String = "foo"
    }

    object Bar {
      implicit val st: String = "bar" 
    }

    def printS(implicit string: String) = println(s"s: ${string}") 
    
    import Foo._
    import Bar._    
    
    implicit val s: String = "ciao"
    printS 
    // WILL PRINT "bar" 

  }  

  hiddenByName2
}