ValueClassDebug.scala

object ValueClassDebug {
  class Foo

  class FooExtNormalClass(val foo: Foo) {
    def bar: Int = 42
  }

  implicit class FooExtImplicitClass(val foo: Foo) {
    def barViaImplicitClass: Int = 42
  }

  implicit class FooExtImplicitValueClass(val foo: Foo) extends AnyVal {
    def barViaImplicitValueClass: Int = 42
  }

  implicit def toFooExt(foo: Foo) = new FooExtAnyVal(foo)
  class FooExtAnyVal(val foo: Foo) extends AnyVal {
    def barViaImplicitDef: Int = 42
  }
}

object Main extends App {
  import ValueClassDebug._
  val foo = new Foo
  
  // explicit instantiation of normal class always results in object allocation
  // new Ext.FooExtNormalClass(this.foo()).bar();
  new FooExtNormalClass(foo).bar 

  // no object allocation when using implicit class (note: no value class)
  // Ext$.MODULE$.FooExtImplicitClass(this.foo()).barViaImplicitClass();
  foo.barViaImplicitClass

  // no object allocation when using implicit value class
  // Ext.FooExtImplicitValueClass$.MODULE$.barViaImplicitValueClass$extension(Ext$.MODULE$.FooExtImplicitValueClass(this.foo()));
  foo.barViaImplicitValueClass

  // no object allocation when using implicit function
  // Ext.FooExtAnyVal$.MODULE$.barViaImplicitDef$extension(Ext$.MODULE$.toFooExt(this.foo()));
  foo.barViaImplicitDef
}