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Scala example source code file (TypeKinds.scala)

This example Scala source code file (TypeKinds.scala) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

array, boolean, byte, char, compiler, double, int, nsc, reference, symbol, typekind, valuetypekind

The TypeKinds.scala Scala example source code

/* NSC -- new Scala compiler
 * Copyright 2005-2013 LAMP/EPFL
 * @author  Martin Odersky
 */

package scala.tools.nsc
package backend
package icode

/* A type case

    case UNIT            =>
    case BOOL            =>
    case BYTE            =>
    case SHORT           =>
    case CHAR            =>
    case INT             =>
    case LONG            =>
    case FLOAT           =>
    case DOUBLE          =>
    case REFERENCE(cls)  =>
    case ARRAY(elem)     =>

*/

trait TypeKinds { self: ICodes =>
  import global._
  import definitions.{ ArrayClass, AnyRefClass, ObjectClass, NullClass, NothingClass, arrayType }

  /** A map from scala primitive Types to ICode TypeKinds */
  lazy val primitiveTypeMap: Map[Symbol, TypeKind] = {
    import definitions._
    Map(
      UnitClass     -> UNIT,
      BooleanClass  -> BOOL,
      CharClass     -> CHAR,
      ByteClass     -> BYTE,
      ShortClass    -> SHORT,
      IntClass      -> INT,
      LongClass     -> LONG,
      FloatClass    -> FLOAT,
      DoubleClass   -> DOUBLE
    )
  }
  /** Reverse map for toType */
  private lazy val reversePrimitiveMap: Map[TypeKind, Symbol] =
    (primitiveTypeMap map (_.swap)).toMap

  /** This class represents a type kind. Type kinds
   * represent the types that the VM know (or the ICode
   * view of what VMs know).
   */
  sealed abstract class TypeKind {
    def maxType(other: TypeKind): TypeKind

    def toType: Type = reversePrimitiveMap get this map (_.tpe) getOrElse {
      this match {
        case REFERENCE(cls) => cls.tpe_*
        case ARRAY(elem)    => arrayType(elem.toType)
        case _              => abort("Unknown type kind.")
      }
    }

    def isReferenceType           = false
    def isArrayType               = false
    def isValueType               = false
    def isBoxedType               = false
    final def isRefOrArrayType    = isReferenceType || isArrayType
    final def isNothingType       = this == NothingReference
    final def isNullType          = this == NullReference
    final def isInterfaceType     = this match {
      case REFERENCE(cls) if cls.isInterface || cls.isTrait => true
      case _                                                => false
    }

    /** On the JVM,
     *    BOOL, BYTE, CHAR, SHORT, and INT
     *  are like Ints for the purposes of calculating the lub.
     */
    def isIntSizedType: Boolean = false

    /** On the JVM, similar to isIntSizedType except that BOOL isn't integral while LONG is. */
    def isIntegralType: Boolean = false

    /** On the JVM, FLOAT and DOUBLE. */
    def isRealType: Boolean = false

    final def isNumericType: Boolean = isIntegralType | isRealType

    /** Simple subtyping check */
    def <:<(other: TypeKind): Boolean

    /**
     * this is directly assignable to other if no coercion or
     * casting is needed to convert this to other. It's a distinct
     * relationship from <:< because on the JVM, BOOL, BYTE, CHAR,
     * SHORT need no coercion to INT even though JVM arrays
     * are covariant, ARRAY[SHORT] is not a subtype of ARRAY[INT]
     */
    final def isAssignabledTo(other: TypeKind): Boolean = other match {
      case INT  => this.isIntSizedType
      case _    => this <:< other
    }

    /** Is this type a category 2 type in JVM terms? (ie, is it LONG or DOUBLE?) */
    def isWideType: Boolean = false

    /** The number of dimensions for array types. */
    def dimensions: Int = 0

    protected def uncomparable(thisKind: String, other: TypeKind): Nothing =
      abort("Uncomparable type kinds: " + thisKind + " with " + other)

    protected def uncomparable(other: TypeKind): Nothing =
      uncomparable(this.toString, other)
  }

  sealed abstract class ValueTypeKind extends TypeKind {
    override def isValueType = true
    override def toString = {
      this.getClass.getName stripSuffix "$" dropWhile (_ != '$') drop 1
    }
    def <:<(other: TypeKind): Boolean = this eq other
  }

  /**
   * The least upper bound of two typekinds. They have to be either
   * REFERENCE or ARRAY kinds.
   *
   * The lub is based on the lub of scala types.
   */
  def lub(a: TypeKind, b: TypeKind): TypeKind = {
    /* The compiler's lub calculation does not order classes before traits.
     * This is apparently not wrong but it is inconvenient, and causes the
     * icode checker to choke when things don't match up.  My attempts to
     * alter the calculation at the compiler level were failures, so in the
     * interests of a working icode checker I'm making the adjustment here.
     *
     * Example where we'd like a different answer:
     *
     *   abstract class Tom
     *   case object Bob extends Tom
     *   case object Harry extends Tom
     *   List(Bob, Harry)  // compiler calculates "Product with Tom" rather than "Tom with Product"
     *
     * Here we make the adjustment by rewinding to a pre-erasure state and
     * sifting through the parents for a class type.
     */
    def lub0(tk1: TypeKind, tk2: TypeKind): Type = enteringUncurry {
      val tp = global.lub(List(tk1.toType, tk2.toType))
      val (front, rest) = tp.parents span (_.typeSymbol.isTrait)

      if (front.isEmpty || rest.isEmpty || rest.head.typeSymbol == ObjectClass) tp
      else rest.head
    }

    def isIntLub = (
      (a == INT && b.isIntSizedType) ||
      (b == INT && a.isIntSizedType)
    )

    if (a == b) a
    else if (a.isNothingType) b
    else if (b.isNothingType) a
    else if (a.isBoxedType || b.isBoxedType) AnyRefReference  // we should do better
    else if (isIntLub) INT
    else if (a.isRefOrArrayType && b.isRefOrArrayType) {
      if (a.isNullType) b
      else if (b.isNullType) a
      else toTypeKind(lub0(a, b))
    }
    else throw new CheckerException("Incompatible types: " + a + " with " + b)
  }

  /** The unit value */
  case object UNIT extends ValueTypeKind {
    def maxType(other: TypeKind) = other match {
      case UNIT | REFERENCE(NothingClass)   => UNIT
      case _                                => uncomparable(other)
    }
  }

  /** A boolean value */
  case object BOOL extends ValueTypeKind {
    override def isIntSizedType = true
    def maxType(other: TypeKind) = other match {
      case BOOL | REFERENCE(NothingClass)   => BOOL
      case _                                => uncomparable(other)
    }
  }

  /** Note that the max of Char/Byte and Char/Short is Int, because
   *  neither strictly encloses the other due to unsignedness.
   *  See ticket #2087 for a consequence.
   */

  /** A 1-byte signed integer */
  case object BYTE extends ValueTypeKind {
    override def isIntSizedType = true
    override def isIntegralType = true
    def maxType(other: TypeKind) = {
      if (other == BYTE || other.isNothingType) BYTE
      else if (other == CHAR) INT
      else if (other.isNumericType) other
      else uncomparable(other)
    }
  }

  /** A 2-byte signed integer */
  case object SHORT extends ValueTypeKind {
    override def isIntSizedType = true
    override def isIntegralType = true
    override def maxType(other: TypeKind) = other match {
      case BYTE | SHORT | REFERENCE(NothingClass) => SHORT
      case CHAR                                   => INT
      case INT | LONG | FLOAT | DOUBLE            => other
      case _                                      => uncomparable(other)
    }
  }

  /** A 2-byte UNSIGNED integer */
  case object CHAR extends ValueTypeKind {
    override def isIntSizedType = true
    override def isIntegralType = true
    override def maxType(other: TypeKind) = other match {
      case CHAR | REFERENCE(NothingClass) => CHAR
      case BYTE | SHORT                   => INT
      case INT | LONG | FLOAT | DOUBLE    => other
      case _                              => uncomparable(other)
    }
  }

  /** A 4-byte signed integer */
  case object INT extends ValueTypeKind {
    override def isIntSizedType = true
    override def isIntegralType = true
    override def maxType(other: TypeKind) = other match {
      case BYTE | SHORT | CHAR | INT | REFERENCE(NothingClass)  => INT
      case LONG | FLOAT | DOUBLE                                => other
      case _                                                    => uncomparable(other)
    }
  }

  /** An 8-byte signed integer */
  case object LONG extends ValueTypeKind {
    override def isIntegralType = true
    override def isWideType = true
    override def maxType(other: TypeKind): TypeKind =
      if (other.isIntegralType || other.isNothingType) LONG
      else if (other.isRealType) DOUBLE
      else uncomparable(other)
  }

  /** A 4-byte floating point number */
  case object FLOAT extends ValueTypeKind {
    override def isRealType = true
    override def maxType(other: TypeKind): TypeKind =
      if (other == DOUBLE) DOUBLE
      else if (other.isNumericType || other.isNothingType) FLOAT
      else uncomparable(other)
  }

  /** An 8-byte floating point number */
  case object DOUBLE extends ValueTypeKind {
    override def isRealType = true
    override def isWideType = true
    override def maxType(other: TypeKind): TypeKind =
      if (other.isNumericType || other.isNothingType) DOUBLE
      else uncomparable(other)
  }

  /** A class type. */
  final case class REFERENCE(cls: Symbol) extends TypeKind {
    override def toString = "REF(" + cls + ")"
    assert(cls ne null,
           "REFERENCE to null class symbol.")
    assert(cls != ArrayClass,
           "REFERENCE to Array is not allowed, should be ARRAY[..] instead")
    assert(cls != NoSymbol,
           "REFERENCE to NoSymbol not allowed!")

    /**
     * Approximate `lub`. The common type of two references is
     * always AnyRef. For 'real' least upper bound wrt to subclassing
     * use method 'lub'.
     */
    override def maxType(other: TypeKind) = other match {
      case REFERENCE(_) | ARRAY(_)  => AnyRefReference
      case _                        => uncomparable("REFERENCE", other)
    }

    /** Checks subtyping relationship. */
    def <:<(other: TypeKind) = isNothingType || (other match {
      case REFERENCE(cls2)  => cls.tpe <:< cls2.tpe
      case ARRAY(_)         => cls == NullClass
      case _                => false
    })
    override def isReferenceType = true
  }

  def ArrayN(elem: TypeKind, dims: Int): ARRAY = {
    assert(dims > 0)
    if (dims == 1) ARRAY(elem)
    else ARRAY(ArrayN(elem, dims - 1))
  }

  final case class ARRAY(elem: TypeKind) extends TypeKind {
    override def toString    = "ARRAY[" + elem + "]"
    override def isArrayType = true
    override def dimensions  = 1 + elem.dimensions

    /** The ultimate element type of this array. */
    def elementKind: TypeKind = elem match {
      case a @ ARRAY(_) => a.elementKind
      case k            => k
    }

    /**
     * Approximate `lub`. The common type of two references is
     * always AnyRef. For 'real' least upper bound wrt to subclassing
     * use method 'lub'.
     */
    override def maxType(other: TypeKind) = other match {
      case ARRAY(elem2) if elem == elem2  => ARRAY(elem)
      case ARRAY(_) | REFERENCE(_)        => AnyRefReference
      case _                              => uncomparable("ARRAY", other)
    }

    /** Array subtyping is covariant, as in Java. Necessary for checking
     *  code that interacts with Java. */
    def <:<(other: TypeKind) = other match {
      case ARRAY(elem2)                         => elem <:< elem2
      case REFERENCE(AnyRefClass | ObjectClass) => true // TODO: platform dependent!
      case _                                    => false
    }
  }

  /** A boxed value. */
  case class BOXED(kind: TypeKind) extends TypeKind {
    override def isBoxedType = true

    override def maxType(other: TypeKind) = other match {
      case BOXED(`kind`)                      => this
      case REFERENCE(_) | ARRAY(_) | BOXED(_) => AnyRefReference
      case _                                  => uncomparable("BOXED", other)
    }

    /** Checks subtyping relationship. */
    def <:<(other: TypeKind) = other match {
      case BOXED(`kind`)                        => true
      case REFERENCE(AnyRefClass | ObjectClass) => true // TODO: platform dependent!
      case _                                    => false
    }
  }

 /**
  * Dummy TypeKind to represent the ConcatClass in a platform-independent
  * way. For JVM it would have been a REFERENCE to 'StringBuffer'.
  */
  case object ConcatClass extends TypeKind {
    override def toString = "ConcatClass"
    def <:<(other: TypeKind): Boolean = this eq other

    /**
     * Approximate `lub`. The common type of two references is
     * always AnyRef. For 'real' least upper bound wrt to subclassing
     * use method 'lub'.
     */
    override def maxType(other: TypeKind) = other match {
      case REFERENCE(_) => AnyRefReference
      case _            => uncomparable(other)
    }
  }

  ////////////////// Conversions //////////////////////////////

  /** Return the TypeKind of the given type
   *
   *  Call to dealiasWiden fixes #3003 (follow type aliases). Otherwise,
   *  arrayOrClassType below would return ObjectReference.
   */
  def toTypeKind(t: Type): TypeKind = t.dealiasWiden match {
    case ThisType(ArrayClass)            => ObjectReference
    case ThisType(sym)                   => REFERENCE(sym)
    case SingleType(_, sym)              => primitiveOrRefType(sym)
    case ConstantType(_)                 => toTypeKind(t.underlying)
    case TypeRef(_, sym, args)           => primitiveOrClassType(sym, args)
    case ClassInfoType(_, _, ArrayClass) => abort("ClassInfoType to ArrayClass!")
    case ClassInfoType(_, _, sym)        => primitiveOrRefType(sym)

    // !!! Iulian says types which make no sense after erasure should not reach here,
    // which includes the ExistentialType, AnnotatedType, RefinedType.  I don't know
    // if the first two cases exist because they do or as a defensive measure, but
    // at the time I added it, RefinedTypes were indeed reaching here.
    case ExistentialType(_, t)           => toTypeKind(t)
    case AnnotatedType(_, t)             => toTypeKind(t)
    case RefinedType(parents, _)         => parents map toTypeKind reduceLeft lub
    // For sure WildcardTypes shouldn't reach here either, but when
    // debugging such situations this may come in handy.
    // case WildcardType                    => REFERENCE(ObjectClass)
    case norm => abort(
      "Unknown type: %s, %s [%s, %s] TypeRef? %s".format(
        t, norm, t.getClass, norm.getClass, t.isInstanceOf[TypeRef]
      )
    )
  }

  /** Return the type kind of a class, possibly an array type.
   */
  private def arrayOrClassType(sym: Symbol, targs: List[Type]) = sym match {
    case ArrayClass       => ARRAY(toTypeKind(targs.head))
    case _ if sym.isClass => newReference(sym)
    case _                =>
      assert(sym.isType, sym) // it must be compiling Array[a]
      ObjectReference
  }
  /** Interfaces have to be handled delicately to avoid introducing
   *  spurious errors, but if we treat them all as AnyRef we lose too
   *  much information.
   */
  private def newReference(sym: Symbol): TypeKind = {
    // Can't call .toInterface (at this phase) or we trip an assertion.
    // See PackratParser#grow for a method which fails with an apparent mismatch
    // between "object PackratParsers$class" and "trait PackratParsers"
    if (sym.isImplClass) {
      // pos/spec-List.scala is the sole failure if we don't check for NoSymbol
      val traitSym = sym.owner.info.decl(tpnme.interfaceName(sym.name))
      if (traitSym != NoSymbol)
        return REFERENCE(traitSym)
    }
    REFERENCE(sym)
  }

  private def primitiveOrRefType(sym: Symbol) =
    primitiveTypeMap.getOrElse(sym, newReference(sym))
  private def primitiveOrClassType(sym: Symbol, targs: List[Type]) =
    primitiveTypeMap.getOrElse(sym, arrayOrClassType(sym, targs))
}

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