record compilation performance

// Compilation time of each commented function on my machine (as repoted by sbt console).

// **********************************************************************
// Test.scala
import shapeless._
import syntax.singleton._

object Test {
  val r =
    ("k01" ->> 1) :: ("k02" ->> 1) :: ("k03" ->> 1) :: ("k04" ->> 1) :: ("k05" ->> 1) ::
    ("k06" ->> 1) :: ("k07" ->> 1) :: ("k08" ->> 1) :: ("k09" ->> 1) :: ("k10" ->> 1) ::
    ("k11" ->> 1) :: ("k12" ->> 1) :: ("k13" ->> 1) :: ("k14" ->> 1) :: ("k15" ->> 1) ::
    ("k16" ->> 1) :: ("k17" ->> 1) :: ("k18" ->> 1) :: ("k19" ->> 1) :: ("k20" ->> 1) ::
    ("k21" ->> 1) :: ("k22" ->> 1) :: ("k23" ->> 1) :: ("k24" ->> 1) :: ("k25" ->> 1) ::
    ("k26" ->> 1) :: ("k27" ->> 1) :: ("k28" ->> 1) :: ("k29" ->> 1) :: ("k30" ->> 1) ::
    ("k31" ->> 1) :: ("k32" ->> 1) :: ("k33" ->> 1) :: ("k34" ->> 1) :: ("k35" ->> 1) :: HNil

  // r get "k01"  // 1s
  // r get "k02"  // 4s
  // r get "k03"  // 7s
  // r get "k04"  // 10s
  // r get "k05"  // 12s
  // r get "k10"  // 21s
  // r get "k20"  // 30s

  // This loops over every field:
  // jsonless.json4s.toJSON(r) // 5s

  // Cost of selecting with HList.select function is constant:
  // val k02 = Witness("k02")
  // r.select[record.FieldType[k02.T, Int]] // 37s
  // val k20 = Witness("k20")
  // r.select[record.FieldType[k20.T, Int]] // 37s
}

// Test2 compares to encoding which was used in sqltyped < 0.4.0.
// Here record is a HList of Tuple2s. Minimal implementation at the end of a gist.
// Compilation times were 3-4 times quicker.

// **********************************************************************
// Test2.scala
import shapeless.HNil
import legacyrecord._

object k01; object k02; object k03; object k04; object k05; object k06; object k07; object k08;
object k09; object k10; object k11; object k12; object k13; object k14; object k15; object k16;
object k17; object k18; object k19; object k20; object k21; object k22; object k23; object k24;
object k25; object k26; object k27; object k28; object k29; object k30; object k31; object k32;
object k33; object k34; object k35

object Test2 {
  val r =
    (k01 -> 1) :: (k02 -> 1) :: (k03 -> 1) :: (k04 -> 1) :: (k05 -> 1) ::
    (k06 -> 1) :: (k07 -> 1) :: (k08 -> 1) :: (k09 -> 1) :: (k10 -> 1) ::
    (k11 -> 1) :: (k12 -> 1) :: (k13 -> 1) :: (k14 -> 1) :: (k15 -> 1) ::
    (k16 -> 1) :: (k17 -> 1) :: (k18 -> 1) :: (k19 -> 1) :: (k20 -> 1) ::
    (k21 -> 1) :: (k22 -> 1) :: (k23 -> 1) :: (k24 -> 1) :: (k25 -> 1) ::
    (k26 -> 1) :: (k27 -> 1) :: (k28 -> 1) :: (k29 -> 1) :: (k30 -> 1) ::
    (k31 -> 1) :: (k32 -> 1) :: (k33 -> 1) :: (k34 -> 1) :: (k35 -> 1) :: HNil

  // r get k01  // 1s
  // r get k02  // 2s
  // r get k03  // 2s
  // r get k04  // 3s
  // r get k05  // 3s
  // r get k10  // 5s
  // r get k20  // 7s
}



// **********************************************************************
// legacyrecord.scala
import shapeless._

object legacyrecord {
  implicit def recordOps[R <: HList](r: R): RecordOps[R] = new RecordOps(r)
}

final class RecordOps[R <: HList](r: R) {
  def lookup[K](implicit lookup: Selector[R, K]): lookup.Out = lookup(r) 
  def get[K](k: K)(implicit lookup0: Selector[R, K]): lookup0.Out = lookup[K] 
}

@annotation.implicitNotFound(msg = "No field ${K} in record ${L}")
trait Selector[L <: HList, K] {
  type Out
  def apply(l : L): Out
}

trait LowPrioritySelector {
  type Aux[L <: HList, K, Out0] = Selector[L, K] { type Out = Out0 }

  implicit def hlistSelect[H, T <: HList, K]
    (implicit st : Selector[T, K]): Aux[H :: T, K, st.Out] =
      new Selector[H :: T, K] {
        type Out = st.Out
        def apply(l : H :: T): Out = st(l.tail)
      }
}

object Selector extends LowPrioritySelector {
  implicit def hlistSelect1[K, V, T <: HList]: Aux[(K, V) :: T, K, V] =
    new Selector[(K, V) :: T, K] {
      type Out = V
      def apply(l : (K, V) :: T): Out = l.head._2
    }
}