add restricted example

caller/shared/src/main/scala/com/thoughtworks/Caller.scala

@@ -6,10 +6,10 @@ import scala.reflect.macros.Context
 final case class Caller[+A](value: A)
 
 object Caller {
-  implicit def generate: Caller[Any] = macro thisCaller
+  implicit def generate[A]: Caller[A] = macro thisCaller[A]
 
-  def thisCaller(c: Context) = {
+  def thisCaller[A](c: Context): c.Expr[Caller[A]] = {
     import c.universe._
-    c.Expr[Caller[Any]](q"new _root_.com.thoughtworks.Caller[this.type](this)")
+    c.Expr[Caller[A]](q"new _root_.com.thoughtworks.Caller[this.type](this)")
   }
 }

caller/shared/src/test/scala/com/thoughtworks/CallerSpec.scala

@@ -1,12 +1,26 @@
 package com.thoughtworks
 
 import org.scalatest.{FreeSpec, Matchers}
+
 object CallerSpec {
   object Foo {
     def call(implicit caller: Caller[_]): String = {
       caller.value.getClass.getName
     }
   }
+
+  class IKnowWhatImDoing
+
+  object Foo2{
+    def runDangerous()(implicit caller: Caller[IKnowWhatImDoing]) = {
+      println(caller.value)
+    }
+  }
+
+  object Bar2 extends IKnowWhatImDoing {
+    Foo2.runDangerous() // ok, prints Bar2
+  }
+
 }
 
 final class CallerSpec extends FreeSpec with Matchers {
@@ -16,4 +30,12 @@ final class CallerSpec extends FreeSpec with Matchers {
     className should be(this.getClass.getName)
   }
 
+  "restricted" in {
+    """
+    object Bar {
+      Foo2.runDangerous()
+    }
+    """ shouldNot typeCheck
+  }
+
 }