tethys.compat.CollectionBuilder.scala Maven / Gradle / Ivy

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package tethys.compat

import scala.collection.{IterableFactory, IterableFactoryDefaults, MapFactory, mutable}
import scala.language.experimental.macros
import scala.language.higherKinds
import scala.reflect.macros.blackbox

trait CollectionBuilder[A, C] {
  def newBuilder: mutable.Builder[A, C]
}

object CollectionBuilder {

  final class IterableFactoryCollectionBuilder[A, C[_]](factory: IterableFactory[C]) extends CollectionBuilder[A, C[A]] {
    override def newBuilder: mutable.Builder[A, C[A]] = factory.newBuilder[A]
  }

  final class MapFactoryCollectionBuilder[K, V, M[_, _]](factory: MapFactory[M]) extends CollectionBuilder[(K, V), M[K, V]] {
    override def newBuilder: mutable.Builder[(K, V), M[K, V]] = factory.newBuilder[K, V]
  }

  implicit def iterableFactoryCollectionBuilder[A, C[X] <: IterableFactoryDefaults[X, C]]: IterableFactoryCollectionBuilder[A, C] = macro CollectionBuilderMacroImpl.fromIterableFactory[A, C]
  implicit def mapFactoryCollectionBuilder[K, V, M[X, Y] <: scala.collection.Map[X, Y]]: CollectionBuilder[(K, V), M[K, V]] = macro CollectionBuilderMacroImpl.fromMapFactory[K, V, M]

  private class CollectionBuilderMacroImpl(val c: blackbox.Context) {
    import c.universe._

    def fromIterableFactory[A, C[X] <: IterableFactoryDefaults[X, C]](implicit A: WeakTypeTag[A], C: WeakTypeTag[C[A]]): Tree = {
      val ref = C.tpe.typeSymbol.companion
      q"new tethys.compat.CollectionBuilder.IterableFactoryCollectionBuilder[${A.tpe}, ${C.tpe}]($ref)"
    }

    def fromMapFactory[K, V, M[X, Y] <: scala.collection.Map[X, Y]](implicit
                                                   K: WeakTypeTag[K],
                                                   V: WeakTypeTag[V],
                                                   M: WeakTypeTag[M[K, V]]): Tree = {
      val ref = M.tpe.typeSymbol.companion
      q"new tethys.compat.CollectionBuilder.MapFactoryCollectionBuilder[${K.tpe}, ${V.tpe}, ${M.tpe}]($ref)"
    }
  }

}