scala macros and structural subtyping

gistfile1.txt

Welcome to Scala version 2.11.4 (Java HotSpot(TM) 64-Bit Server VM, Java 1.7.0_67).
Type in expressions to have them evaluated.
Type :help for more information.
 
scala> :paste
// Entering paste mode (ctrl-D to finish)
 
import scala.language.experimental.macros
import scala.reflect.macros.Context
  
object A {
  def impl(c: Context): c.Expr[Int] = {
    import c.universe._
    c.Expr[Int](Literal(Constant(2)))
  }
}
 
class A {
  def x: Int = macro A.impl
}
 
 
// Exiting paste mode, now interpreting.
 
warning: there was one deprecation warning; re-run with -deprecation for details
import scala.language.experimental.macros
import scala.reflect.macros.Context
defined object A
defined class A
 
scala> val a0 = new A
a0: A = A@34aad3ab
 
scala> a0.x
res0: Int = 2
 
scala> val a1: {def x: Int} = a0
a1: AnyRef{def x: Int} = A@34aad3ab
 
scala> a1.x
warning: there was one feature warning; re-run with -feature for details
java.lang.NoSuchMethodException: A.x()
  at java.lang.Class.getMethod(Class.java:1665)
  at .reflMethod$Method1(<console>:16)
  ... 33 elided