AutoThingy

autoThingy.scala

import shapeless._

trait Thingy[T] { def stringy(t:T): String }

implicit def autoThingy[T <: Product](implicit gen: LabelledGeneric[T]) : Thingy[T] = new Thingy[T] {
  def toRecord[T <: Product, Repr](obj: T)(implicit lg: LabelledGeneric.Aux[T, Repr]): Repr = lg.to(obj)
  def stringy(t: T) = {
    val rec = toRecord(t)
    val keys = rec.keys
    keys.mkString
  }
}
/*
error: type mismatch;
 found   : shapeless.LabelledGeneric[T]
 required: shapeless.LabelledGeneric.Aux[T,this.Repr]
    (which expands to)  shapeless.LabelledGeneric[T]{type Repr = this.Repr}
       val rec = toRecord(t)
                         ^
error: value keys is not a member of this.Repr
       val keys = rec.keys
                      ^
*/

implicit def autoThingy2[T <: Product, Repr](implicit gen: LabelledGeneric.Aux[T,Repr]) : Thingy[T] = new Thingy[T] {
  def stringy(t: T) = {
    val rec = gen.to(t)
    val keys = rec.keys
    keys.mkString
  }
}
/*
error: value keys is not a member of type parameter gen.Repr
       val keys = rec.keys
                      ^
*/

implicit def autoThingy3[T <: Product] : Thingy[T] = new Thingy[T] {
  def toRecord[Repr](t: T)(implicit gen: LabelledGeneric.Aux[T,Repr]): Repr = gen.to(t)
  
  def stringy(t: T) = {
    val rec = toRecord(t)
    val keys = rec.keys
    keys.mkString
  }
}
/*
error: could not find implicit value for parameter gen: shapeless.LabelledGeneric.Aux[T,Repr]
       val rec = toRecord(t)
                         ^
*/

implicit def autoThingy3[T <: Product : LabelledGeneric] : Thingy[T] = new Thingy[T] {
  def toRecord[Repr](t: T)(implicit gen: LabelledGeneric.Aux[T,Repr]): Repr = gen.to(t)
  
  def stringy(t: T) = {
    val rec = toRecord(t)
    val keys = rec.keys
    keys.mkString
  }
}
/*
error: type mismatch;
 found   : shapeless.LabelledGeneric[T]
 required: shapeless.LabelledGeneric.Aux[T,this.Repr]
    (which expands to)  shapeless.LabelledGeneric[T]{type Repr = this.Repr}
       val rec = toRecord(t)
                         ^
error: value keys is not a member of this.Repr
          val keys = rec.keys
                         ^
*/

implicit def autoThingy4[T <: Product](implicit gen: LabelledGeneric[T]) : Thingy[T] = new Thingy[T] {
  def toRecord[T2 <: Product, Repr](obj: T2)(implicit lg: LabelledGeneric.Aux[T2, Repr]): Repr = lg.to(obj)
  def stringy(t: T) = {
    val rec = toRecord(t)
    val keys = rec.keys
    keys.mkString
  }
}
/*
error: type mismatch;
 found   : shapeless.LabelledGeneric[T]
 required: shapeless.LabelledGeneric.Aux[T,this.Repr]
    (which expands to)  shapeless.LabelledGeneric[T]{type Repr = this.Repr}
           val rec = toRecord(t)
                             ^
error: value keys is not a member of this.Repr
           val keys = rec.keys
                          ^
*/