gistfile1.scala

scala> :paste
// Entering paste mode (ctrl-D to finish)

import scala.language.dynamics
import scala.language.experimental.macros

import scala.reflect.macros.whitebox

object implicitly extends Dynamic {
  def apply[T](implicit t: T): T {} = t

  def selectDynamic(tpeTree: String): Any = macro implicitlyImpl

  def implicitlyImpl(c: whitebox.Context)(tpeTree: c.Tree): c.Tree = {
    import c.universe._
    import internal._, decorators._

    val q"${tpeString: String}" = tpeTree
    val parsed = c.parse("null : "+tpeString)
    val tpe = c.typecheck(parsed, mode = c.TYPEmode).tpe
    val inferred = c.inferImplicitValue(tpe)

    Literal(Constant(null)).setType(inferred.tpe)
  }
}

// Exiting paste mode, now interpreting.

import scala.language.dynamics
import scala.language.experimental.macros
import scala.reflect.macros.whitebox
defined object implicitly

scala> :paste
// Entering paste mode (ctrl-D to finish)
                                                                                                                                            
trait Foo[T] { type U }                                                                                                                     
implicit def fooSI: Foo[String] { type U = Int } = new Foo[String] { type U = Int }                                                         
implicit def fooDB: Foo[Double] { type U = Boolean } = new Foo[Double] { type U = Boolean }                                                 
                                                                                                                                            
// Exiting paste mode, now interpreting.                                                                                                    
                                                                                                                                            
defined trait Foo                                                                                                                           
fooSI: Foo[String]{type U = Int}                                                                                                            
fooDB: Foo[Double]{type U = Boolean}                                                                                                        
                                                                                                                                            
scala> implicitly[Foo[String]] // Summon values, as usual
res0: Foo[String] = $anon$1@357dc417                                                                                                        
                                                                                                                                            
scala> implicitly[Foo[Double]] // Summon values, as usual
res1: Foo[Double] = $anon$2@4f9b02ed                                                                                                        
                                                                                                                                            
scala> val i: implicitly.`Foo[String]`.U = 23 // But it's also a stable prefix for a type
i: Int = 23                                                                                                                                 
                                                                                                                                            
scala> val b: implicitly.`Foo[Double]`.U = true // But it's also a stable prefix for a type
b: Boolean = true