japgolly.microlibs.compiletime.Field.scala Maven / Gradle / Ivy

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compileTime

There is a newer version: 4.2.1

package japgolly.microlibs.compiletime

import scala.deriving.*
import scala.quoted.*
import MacroEnv.*

trait Field {
  type Name
  type Type

  val idx: Int
  val name: String
  def showType: String
  implicit val typeInstance: scala.quoted.Type[Type]

  override def toString = s"[Field $idx] $name: $showType"

  final def typeRepr(using q: Quotes): q.reflect.TypeRepr =
    q.reflect.TypeRepr.of(using typeInstance)

  final def onProduct[P](p: Expr[P])(using Quotes, scala.quoted.Type[P]): Expr[Type] =
    '{ $p.asInstanceOf[Product].productElement(${Expr(idx)}).asInstanceOf[Type] }
}

object Fields {

  def summonFromMirror[A: Type](using Quotes): List[Field] =
    fromMirror(Expr.summonOrError[Mirror.Of[A]])

  def fromMirror[A: Type](m: Expr[Mirror.Of[A]])(using Quotes): List[Field] = {
    import quotes.reflect.*

    def go[Ls: Type, Ts: Type](idx: Int): List[Field] =
      (Type.of[Ls], Type.of[Ts]) match
        case ('[l *: ll], '[t *: tt]) =>
          val t = Type.of[t]
          val _idx = idx
          val _name = TypeRepr.of[l] match
            case ConstantType(StringConstant(n)) => n
            case _                               => "?"
          val f: Field = new Field {
            override type Name                 = l
            override type Type                 = t
            override val idx                   = _idx
            override val name                  = _name
            override def showType              = Type.show[t]
            override implicit val typeInstance = t
          }
          f :: go[ll, tt](idx + 1)

        case ('[EmptyTuple], _) =>
          Nil

    m match
      case '{ $m: Mirror.ProductOf[A] { type MirroredElemLabels = ls; type MirroredElemTypes = ts }} =>
        go[ls, ts](0)
      case '{ $m: Mirror.SumOf[A] { type MirroredElemLabels = ls; type MirroredElemTypes = ts }} =>
        go[ls, ts](0)
  }

}