path: root/src/library/scala/reflect/Manifest.scala

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2007-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala.reflect

import scala.collection.mutable.{ ArrayBuilder, WrappedArray }
import mirror._

/** A `Manifest[T]` is an opaque descriptor for type T.  Its supported use
 *  is to give access to the erasure of the type as a `Class` instance, as
 *  is necessary for the creation of native `Arrays` if the class is not
 *  known at compile time.
 *
 *  The type-relation operators `<:<` and `=:=` should be considered
 *  approximations only, as there are numerous aspects of type conformance
 *  which are not yet adequately represented in manifests.
 *
 *  Example usages:
{{{
  def arr[T] = new Array[T](0)                          // does not compile
  def arr[T](implicit m: Manifest[T]) = new Array[T](0) // compiles
  def arr[T: Manifest] = new Array[T](0)                // shorthand for the preceding

  // Methods manifest, classManifest, and optManifest are in [[scala.Predef]].
  def isApproxSubType[T: Manifest, U: Manifest] = manifest[T] <:< manifest[U]
  isApproxSubType[List[String], List[AnyRef]] // true
  isApproxSubType[List[String], List[Int]]    // false

  def methods[T: ClassManifest] = classManifest[T].erasure.getMethods
  def retType[T: ClassManifest](name: String) =
    methods[T] find (_.getName == name) map (_.getGenericReturnType)

  retType[Map[_, _]]("values")  // Some(scala.collection.Iterable<B>)
}}}
 *
 */
@annotation.implicitNotFound(msg = "No Manifest available for ${T}.")
trait Manifest[T] extends ClassManifest[T] with Equals {
  override def typeArguments: List[Manifest[_]] = Nil

  override def arrayManifest: Manifest[Array[T]] =
    Manifest.classType[Array[T]](arrayClass[T](erasure), this)

  override def canEqual(that: Any): Boolean = that match {
    case _: Manifest[_]   => true
    case _                => false
  }
  /** Note: testing for erasure here is important, as it is many times
   *  faster than <:< and rules out most comparisons.
   */
  override def equals(that: Any): Boolean = that match {
    case m: Manifest[_] => (m canEqual this) && (this.erasure == m.erasure) && (this <:< m) && (m <:< this)
    case _              => false
  }
  override def hashCode = this.erasure.##
}

sealed abstract class AnyValManifest[T <: AnyVal](override val toString: String) extends Manifest[T] with Equals {
  override def <:<(that: ClassManifest[_]): Boolean =
    (that eq this) || (that eq Manifest.Any) || (that eq Manifest.AnyVal)
  override def canEqual(other: Any) = other match {
    case _: AnyValManifest[_] => true
    case _                    => false
  }
  override def equals(that: Any): Boolean = this eq that.asInstanceOf[AnyRef]
  override val hashCode = System.identityHashCode(this)
}

/** The object `Manifest` defines factory methods for manifests.
 *  It is intended for use by the compiler and should not be used
 *  in client code.
 */
object Manifest {
  def valueManifests: List[AnyValManifest[_]] =
    List(Byte, Short, Char, Int, Long, Float, Double, Boolean, Unit)

  val Byte: AnyValManifest[Byte] = new AnyValManifest[scala.Byte]("Byte") {
    def erasure = java.lang.Byte.TYPE
    override def newArray(len: Int): Array[Byte] = new Array[Byte](len)
    override def newWrappedArray(len: Int): WrappedArray[Byte] = new WrappedArray.ofByte(new Array[Byte](len))
    override def newArrayBuilder(): ArrayBuilder[Byte] = new ArrayBuilder.ofByte()
    private def readResolve(): Any = Manifest.Byte
  }

  val Short: AnyValManifest[Short] = new AnyValManifest[scala.Short]("Short") {
    def erasure = java.lang.Short.TYPE
    override def newArray(len: Int): Array[Short] = new Array[Short](len)
    override def newWrappedArray(len: Int): WrappedArray[Short] = new WrappedArray.ofShort(new Array[Short](len))
    override def newArrayBuilder(): ArrayBuilder[Short] = new ArrayBuilder.ofShort()
    private def readResolve(): Any = Manifest.Short
  }

  val Char: AnyValManifest[Char] = new AnyValManifest[scala.Char]("Char") {
    def erasure = java.lang.Character.TYPE
    override def newArray(len: Int): Array[Char] = new Array[Char](len)
    override def newWrappedArray(len: Int): WrappedArray[Char] = new WrappedArray.ofChar(new Array[Char](len))
    override def newArrayBuilder(): ArrayBuilder[Char] = new ArrayBuilder.ofChar()
    private def readResolve(): Any = Manifest.Char
  }

  val Int: AnyValManifest[Int] = new AnyValManifest[scala.Int]("Int") {
    def erasure = java.lang.Integer.TYPE
    override def newArray(len: Int): Array[Int] = new Array[Int](len)
    override def newWrappedArray(len: Int): WrappedArray[Int] = new WrappedArray.ofInt(new Array[Int](len))
    override def newArrayBuilder(): ArrayBuilder[Int] = new ArrayBuilder.ofInt()
    private def readResolve(): Any = Manifest.Int
  }

  val Long: AnyValManifest[Long] = new AnyValManifest[scala.Long]("Long") {
    def erasure = java.lang.Long.TYPE
    override def newArray(len: Int): Array[Long] = new Array[Long](len)
    override def newWrappedArray(len: Int): WrappedArray[Long] = new WrappedArray.ofLong(new Array[Long](len))
    override def newArrayBuilder(): ArrayBuilder[Long] = new ArrayBuilder.ofLong()
    private def readResolve(): Any = Manifest.Long
  }

  val Float: AnyValManifest[Float] = new AnyValManifest[scala.Float]("Float") {
    def erasure = java.lang.Float.TYPE
    override def newArray(len: Int): Array[Float] = new Array[Float](len)
    override def newWrappedArray(len: Int): WrappedArray[Float] = new WrappedArray.ofFloat(new Array[Float](len))
    override def newArrayBuilder(): ArrayBuilder[Float] = new ArrayBuilder.ofFloat()
    private def readResolve(): Any = Manifest.Float
  }

  val Double: AnyValManifest[Double] = new AnyValManifest[scala.Double]("Double") {
    def erasure = java.lang.Double.TYPE
    override def newArray(len: Int): Array[Double] = new Array[Double](len)
    override def newWrappedArray(len: Int): WrappedArray[Double] = new WrappedArray.ofDouble(new Array[Double](len))
    override def newArrayBuilder(): ArrayBuilder[Double] = new ArrayBuilder.ofDouble()
    private def readResolve(): Any = Manifest.Double
  }

  val Boolean: AnyValManifest[Boolean] = new AnyValManifest[scala.Boolean]("Boolean") {
    def erasure = java.lang.Boolean.TYPE
    override def newArray(len: Int): Array[Boolean] = new Array[Boolean](len)
    override def newWrappedArray(len: Int): WrappedArray[Boolean] = new WrappedArray.ofBoolean(new Array[Boolean](len))
    override def newArrayBuilder(): ArrayBuilder[Boolean] = new ArrayBuilder.ofBoolean()
    private def readResolve(): Any = Manifest.Boolean
  }

  val Unit: AnyValManifest[Unit] = new AnyValManifest[scala.Unit]("Unit") {
    def erasure = java.lang.Void.TYPE
    override def newArray(len: Int): Array[Unit] = new Array[Unit](len)
    override def newWrappedArray(len: Int): WrappedArray[Unit] = new WrappedArray.ofUnit(new Array[Unit](len))
    override def newArrayBuilder(): ArrayBuilder[Unit] = new ArrayBuilder.ofUnit()
    private def readResolve(): Any = Manifest.Unit
  }

  val Any: Manifest[scala.Any] = new PhantomManifest[scala.Any]("Any") {
    override def <:<(that: ClassManifest[_]): Boolean = (that eq this)
    private def readResolve(): Any = Manifest.Any
  }

  val Object: Manifest[java.lang.Object] = new PhantomManifest[java.lang.Object]("Object") {
    override def <:<(that: ClassManifest[_]): Boolean = (that eq this) || (that eq Any)
    private def readResolve(): Any = Manifest.Object
  }

  val AnyVal: Manifest[scala.AnyVal] = new PhantomManifest[scala.AnyVal]("AnyVal") {
    override def <:<(that: ClassManifest[_]): Boolean = (that eq this) || (that eq Any)
    private def readResolve(): Any = Manifest.AnyVal
  }

  val Null: Manifest[scala.Null] = new PhantomManifest[scala.Null]("Null") {
    override def <:<(that: ClassManifest[_]): Boolean =
      (that ne null) && (that ne Nothing) && !(that <:< AnyVal)
    private def readResolve(): Any = Manifest.Null
  }

  val Nothing: Manifest[scala.Nothing] = new PhantomManifest[scala.Nothing]("Nothing") {
    override def <:<(that: ClassManifest[_]): Boolean = (that ne null)
    private def readResolve(): Any = Manifest.Nothing
  }

  private class SingletonTypeManifest[T <: AnyRef](value: AnyRef) extends Manifest[T] {
    lazy val erasure = value.getClass
    override lazy val tpe = mirror.SingleType(mirror.NoPrefix, InstanceRefSymbol(value)) // todo: change to freevar
    override lazy val toString = value.toString + ".type"
  }

  /** Manifest for the singleton type `value.type`. */
  def singleType[T <: AnyRef](value: AnyRef): Manifest[T] =
    new SingletonTypeManifest[T](value)

  /** Manifest for the class type `clazz[args]`, where `clazz` is
    * a top-level or static class.
    * @note This no-prefix, no-arguments case is separate because we
    *       it's called from ScalaRunTime.boxArray itself. If we
    *       pass varargs as arrays into this, we get an infinitely recursive call
    *       to boxArray. (Besides, having a separate case is more efficient)
    */
  def classType[T](clazz: Predef.Class[_]): Manifest[T] =
    new ClassTypeManifest[T](None, clazz, Nil)

  /** Manifest for the class type `clazz`, where `clazz` is
    * a top-level or static class and args are its type arguments. */
  def classType[T](clazz: Predef.Class[T], arg1: Manifest[_], args: Manifest[_]*): Manifest[T] =
    new ClassTypeManifest[T](None, clazz, arg1 :: args.toList)

  /** Manifest for the class type `clazz[args]`, where `clazz` is
    * a class with non-package prefix type `prefix` and type arguments `args`.
    */
  def classType[T](prefix: Manifest[_], clazz: Predef.Class[_], args: Manifest[_]*): Manifest[T] =
    new ClassTypeManifest[T](Some(prefix), clazz, args.toList)

  private abstract class PhantomManifest[T](override val toString: String) extends ClassTypeManifest[T](None, classOf[java.lang.Object], Nil) {
    override def equals(that: Any): Boolean = this eq that.asInstanceOf[AnyRef]
    override val hashCode = System.identityHashCode(this)
  }

  /** Manifest for the class type `clazz[args]`, where `clazz` is
    * a top-level or static class. */
  private class ClassTypeManifest[T](prefix: Option[Manifest[_]],
                                     val erasure: Predef.Class[_],
                                     override val typeArguments: List[Manifest[_]]) extends Manifest[T] {
    override lazy val tpe = {
      val clazz = classToSymbol(erasure)
      val pre = prefix match {
        case Some(pm) => pm.tpe
        case None => clazz.owner.thisType
      }
      namedType(pre, clazz, typeArguments map (_.tpe))
    }

    override def toString =
      (if (prefix.isEmpty) "" else prefix.get.toString+"#") +
      (if (erasure.isArray) "Array" else erasure.getName) +
      argString
   }

  def arrayType[T](arg: Manifest[_]): Manifest[Array[T]] =
    arg.asInstanceOf[Manifest[T]].arrayManifest

  /** Manifest for the abstract type `prefix # name'. `upperBound` is not
    * strictly necessary as it could be obtained by reflection. It was
    * added so that erasure can be calculated without reflection. */
  def abstractType[T](prefix: Manifest[_], name: String, upperBound: Predef.Class[_], args: Manifest[_]*): Manifest[T] =
    new Manifest[T] {
      def erasure = upperBound
      override lazy val tpe = namedType(prefix.tpe, prefix.tpe.member(newTypeName(name)), args map (_.tpe) toList)
      override val typeArguments = args.toList
      override def toString = prefix.toString+"#"+name+argString
    }

  /** Manifest for the unknown type `_ >: L <: U` in an existential.
    */
  def wildcardType[T](lowerBound: Manifest[_], upperBound: Manifest[_]): Manifest[T] =
    new Manifest[T] {
      def erasure = upperBound.erasure
      override lazy val tpe = mirror.TypeBounds(lowerBound.tpe, upperBound.tpe)
      override def toString =
        "_" +
        (if (lowerBound eq Nothing) "" else " >: "+lowerBound) +
        (if (upperBound eq Nothing) "" else " <: "+upperBound)
    }

  /** Manifest for the intersection type `parents_0 with ... with parents_n'. */
  def intersectionType[T](parents: Manifest[_]*): Manifest[T] =
    new Manifest[T] {
      def erasure = parents.head.erasure
      override lazy val tpe = mirror.RefinedType((parents map (_.tpe)).toList, newScope)
      override def toString = parents.mkString(" with ")
    }

  /** A generic manifest factory from a reflect.Type. Except where
   *  mandated by performance considerations, we should replace most
   *  other manifest factories by this one. There's just one thing
   *  that needs to be done first: A Manifest's type can refer
   *  to type variables that are controlled by manifests. In that
   *  case the reified type needs to contain the type passed in the manifest
   *  instead of the reference to the manifest. Note that splicing manifests
   *  into manfifests is completely analogous to splicing code blocks into
   *  code blocks. Manifest[T] and Code[T] are really the same thing, only one
   *  works for types, the other for trees.
   *  Another complication is that once we generate manifests from types, we really
   *  should have reflection as a standard component shipped with the standard library,
   *  instead of in scala-compiler.jar.
   */
  def apply[T](_tpe: mirror.Type): Manifest[T] = new Manifest[T] {
    override lazy val tpe = _tpe
    override def erasure = mirror.typeToClass(_tpe.erasedType)
    override def toString = _tpe.toString
  }
}