Scala example source code file (Predef.scala)

This example Scala source code file (Predef.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

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a, a, any, array, array, arrayops, b, b, boolean, char, el2, int, int, string

The Scala Predef.scala source code

/*                     __                                               *\
**     ________ ___   / /  ___     Scala API                            **
**    / __/ __// _ | / /  / _ |    (c) 2002-2011, LAMP/EPFL             **
**  __\ \/ /__/ __ |/ /__/ __ |    http://scala-lang.org/               **
** /____/\___/_/ |_/____/_/ | |                                         **
**                          |/                                          **
\*                                                                      */

package scala

import scala.collection.{ mutable, immutable, generic }
import immutable.StringOps
import mutable.ArrayOps
import generic.CanBuildFrom
import annotation.{ elidable, implicitNotFound }
import annotation.elidable.ASSERTION

/** The <code>Predef object provides definitions that are
 *  accessible in all Scala compilation units without explicit
 *  qualification.
 */
object Predef extends LowPriorityImplicits {
  /** Return the runtime representation of a class type.  This is a stub method.
   *  The actual implementation is filled in by the compiler.
   */
  def classOf[T]: Class[T] = null

  type String        = java.lang.String
  type Class[T]      = java.lang.Class[T]

  // miscelleaneous -----------------------------------------------------
  scala.`package`                         // to force scala package object to be seen.
  scala.collection.immutable.List         // to force Nil, :: to be seen.

  type Function[-A, +B] = Function1[A, B]
    
  type Map[A, +B] = immutable.Map[A, B]
  type Set[A]     = immutable.Set[A]
  val Map         = immutable.Map
  val Set         = immutable.Set
  val AnyRef      = new SpecializableCompanion {}   // a dummy used by the specialization annotation

  // Manifest types, companions, and incantations for summoning
  type ClassManifest[T] = scala.reflect.ClassManifest[T]
  type Manifest[T]      = scala.reflect.Manifest[T]
  type OptManifest[T]   = scala.reflect.OptManifest[T]
  val ClassManifest     = scala.reflect.ClassManifest
  val Manifest          = scala.reflect.Manifest
  val NoManifest        = scala.reflect.NoManifest
  
  def manifest[T](implicit m: Manifest[T])           = m
  def classManifest[T](implicit m: ClassManifest[T]) = m
  def optManifest[T](implicit m: OptManifest[T])     = m

  // Minor variations on identity functions
  def identity[A](x: A): A         = x    // @see `conforms` for the implicit version
  def implicitly[T](implicit e: T) = e    // for summoning implicit values from the nether world
  @inline def locally[T](x: T): T  = x    // to communicate intent and avoid unmoored statements
  
  // Apparently needed for the xml library
  val $scope = scala.xml.TopScope

  // Deprecated

  @deprecated("Use sys.error(message) instead", "2.9.0")
  def error(message: String): Nothing = sys.error(message)

  @deprecated("Use sys.exit() instead", "2.9.0")
  def exit(): Nothing = sys.exit()

  @deprecated("Use sys.exit(status) instead", "2.9.0")
  def exit(status: Int): Nothing = sys.exit(status)

  @deprecated("Use formatString.format(args: _*) or arg.formatted(formatString) instead", "2.9.0")
  def format(text: String, xs: Any*) = augmentString(text).format(xs: _*)

  // errors and asserts -------------------------------------------------

  /** Tests an expression, throwing an AssertionError if false.
   *  Calls to this method will not be generated if -Xelide-below
   *  is at least ASSERTION.
   *
   *  @see elidable
   *  @param p   the expression to test
   */
  @elidable(ASSERTION)
  def assert(assertion: Boolean) {
    if (!assertion)
      throw new java.lang.AssertionError("assertion failed")
  }

  /** Tests an expression, throwing an AssertionError if false.
   *  Calls to this method will not be generated if -Xelide-below
   *  is at least ASSERTION.
   *
   *  @see elidable
   *  @param p   the expression to test
   *  @param msg a String to include in the failure message
   */
  @elidable(ASSERTION) @inline
  final def assert(assertion: Boolean, message: => Any) {
    if (!assertion)
      throw new java.lang.AssertionError("assertion failed: "+ message)
  }

  /** Tests an expression, throwing an AssertionError if false.
   *  This method differs from assert only in the intent expressed:
   *  assert contains a predicate which needs to be proven, while
   *  assume contains an axiom for a static checker.  Calls to this method
   *  will not be generated if -Xelide-below is at least ASSERTION.
   *
   *  @see elidable
   *  @param p   the expression to test
   */
  @elidable(ASSERTION)
  def assume(assumption: Boolean) {
    if (!assumption)
      throw new java.lang.AssertionError("assumption failed")
  }

  /** Tests an expression, throwing an AssertionError if false.
   *  This method differs from assert only in the intent expressed:
   *  assert contains a predicate which needs to be proven, while
   *  assume contains an axiom for a static checker.  Calls to this method
   *  will not be generated if -Xelide-below is at least ASSERTION.
   *
   *  @see elidable
   *  @param p   the expression to test
   *  @param msg a String to include in the failure message
   */
  @elidable(ASSERTION) @inline
  final def assume(assumption: Boolean, message: => Any) {
    if (!assumption)
      throw new java.lang.AssertionError("assumption failed: "+ message)
  }

  /** Tests an expression, throwing an IllegalArgumentException if false.
   *  This method is similar to assert, but blames the caller of the method
   *  for violating the condition.
   *
   *  @param p   the expression to test
   */
  def require(requirement: Boolean) {
    if (!requirement)
      throw new IllegalArgumentException("requirement failed")
  }

  /** Tests an expression, throwing an IllegalArgumentException if false.
   *  This method is similar to assert, but blames the caller of the method
   *  for violating the condition.
   *
   *  @param p   the expression to test
   *  @param msg a String to include in the failure message
   */
  @inline final def require(requirement: Boolean, message: => Any) {
    if (!requirement)
      throw new IllegalArgumentException("requirement failed: "+ message)
  }

  final class Ensuring[A](val x: A) {
    def ensuring(cond: Boolean): A = { assert(cond); x }
    def ensuring(cond: Boolean, msg: => Any): A = { assert(cond, msg); x }
    def ensuring(cond: A => Boolean): A = { assert(cond(x)); x }
    def ensuring(cond: A => Boolean, msg: => Any): A = { assert(cond(x), msg); x }
  }
  implicit def any2Ensuring[A](x: A): Ensuring[A] = new Ensuring(x)

  // tupling ------------------------------------------------------------

  type Pair[+A, +B] = Tuple2[A, B]
  object Pair {
    def apply[A, B](x: A, y: B) = Tuple2(x, y)
    def unapply[A, B](x: Tuple2[A, B]): Option[Tuple2[A, B]] = Some(x)
  }

  type Triple[+A, +B, +C] = Tuple3[A, B, C]
  object Triple {
    def apply[A, B, C](x: A, y: B, z: C) = Tuple3(x, y, z)
    def unapply[A, B, C](x: Tuple3[A, B, C]): Option[Tuple3[A, B, C]] = Some(x)
  }

  final class ArrowAssoc[A](val x: A) {
    @inline def -> [B](y: B): Tuple2[A, B] = Tuple2(x, y)
    def →[B](y: B): Tuple2[A, B] = ->(y)
  }
  implicit def any2ArrowAssoc[A](x: A): ArrowAssoc[A] = new ArrowAssoc(x)

  // printing and reading -----------------------------------------------

  def print(x: Any) = Console.print(x)
  def println() = Console.println()
  def println(x: Any) = Console.println(x)
  def printf(text: String, xs: Any*) = Console.print(text.format(xs: _*))

  def readLine(): String = Console.readLine()
  def readLine(text: String, args: Any*) = Console.readLine(text, args)
  def readBoolean() = Console.readBoolean()
  def readByte() = Console.readByte()
  def readShort() = Console.readShort()
  def readChar() = Console.readChar()
  def readInt() = Console.readInt()
  def readLong() = Console.readLong()
  def readFloat() = Console.readFloat()
  def readDouble() = Console.readDouble()
  def readf(format: String) = Console.readf(format)
  def readf1(format: String) = Console.readf1(format)
  def readf2(format: String) = Console.readf2(format)
  def readf3(format: String) = Console.readf3(format)
  
  // views --------------------------------------------------------------

  implicit def exceptionWrapper(exc: Throwable) = new runtime.RichException(exc)
  
  implicit def zipped2ToTraversable[El1, El2](zz: Tuple2[_, _]#Zipped[_, El1, _, El2]): Traversable[(El1, El2)] =
    new Traversable[(El1, El2)] {
      def foreach[U](f: ((El1, El2)) => U): Unit = zz foreach Function.untupled(f)
    }

  implicit def zipped3ToTraversable[El1, El2, El3](zz: Tuple3[_, _, _]#Zipped[_, El1, _, El2, _, El3]): Traversable[(El1, El2, El3)] =
    new Traversable[(El1, El2, El3)] {
      def foreach[U](f: ((El1, El2, El3)) => U): Unit = zz foreach Function.untupled(f)
    }

  implicit def genericArrayOps[T](xs: Array[T]): ArrayOps[T] = xs match {
    case x: Array[AnyRef]  => refArrayOps[AnyRef](x).asInstanceOf[ArrayOps[T]]
    case x: Array[Int]     => intArrayOps(x).asInstanceOf[ArrayOps[T]]
    case x: Array[Double]  => doubleArrayOps(x).asInstanceOf[ArrayOps[T]]
    case x: Array[Long]    => longArrayOps(x).asInstanceOf[ArrayOps[T]]
    case x: Array[Float]   => floatArrayOps(x).asInstanceOf[ArrayOps[T]]
    case x: Array[Char]    => charArrayOps(x).asInstanceOf[ArrayOps[T]]
    case x: Array[Byte]    => byteArrayOps(x).asInstanceOf[ArrayOps[T]] 
    case x: Array[Short]   => shortArrayOps(x).asInstanceOf[ArrayOps[T]]
    case x: Array[Boolean] => booleanArrayOps(x).asInstanceOf[ArrayOps[T]]
    case x: Array[Unit]    => unitArrayOps(x).asInstanceOf[ArrayOps[T]]
    case null              => null
  }
  
  implicit def refArrayOps[T <: AnyRef](xs: Array[T]): ArrayOps[T] = new ArrayOps.ofRef[T](xs)
  implicit def intArrayOps(xs: Array[Int]): ArrayOps[Int] = new ArrayOps.ofInt(xs)
  implicit def doubleArrayOps(xs: Array[Double]): ArrayOps[Double] = new ArrayOps.ofDouble(xs)
  implicit def longArrayOps(xs: Array[Long]): ArrayOps[Long] = new ArrayOps.ofLong(xs)
  implicit def floatArrayOps(xs: Array[Float]): ArrayOps[Float] = new ArrayOps.ofFloat(xs)
  implicit def charArrayOps(xs: Array[Char]): ArrayOps[Char] = new ArrayOps.ofChar(xs)
  implicit def byteArrayOps(xs: Array[Byte]): ArrayOps[Byte] = new ArrayOps.ofByte(xs)
  implicit def shortArrayOps(xs: Array[Short]): ArrayOps[Short] = new ArrayOps.ofShort(xs)
  implicit def booleanArrayOps(xs: Array[Boolean]): ArrayOps[Boolean] = new ArrayOps.ofBoolean(xs)
  implicit def unitArrayOps(xs: Array[Unit]): ArrayOps[Unit] = new ArrayOps.ofUnit(xs)

  // Primitive Widenings --------------------------------------------------------------

  implicit def byte2short(x: Byte): Short = x.toShort
  implicit def byte2int(x: Byte): Int = x.toInt
  implicit def byte2long(x: Byte): Long = x.toLong
  implicit def byte2float(x: Byte): Float = x.toFloat
  implicit def byte2double(x: Byte): Double = x.toDouble

  implicit def short2int(x: Short): Int = x.toInt
  implicit def short2long(x: Short): Long = x.toLong
  implicit def short2float(x: Short): Float = x.toFloat
  implicit def short2double(x: Short): Double = x.toDouble

  implicit def char2int(x: Char): Int = x.toInt
  implicit def char2long(x: Char): Long = x.toLong
  implicit def char2float(x: Char): Float = x.toFloat
  implicit def char2double(x: Char): Double = x.toDouble

  implicit def int2long(x: Int): Long = x.toLong
  implicit def int2float(x: Int): Float = x.toFloat
  implicit def int2double(x: Int): Double = x.toDouble

  implicit def long2float(x: Long): Float = x.toFloat
  implicit def long2double(x: Long): Double = x.toDouble

  implicit def float2double(x: Float): Double = x.toDouble
  
  // "Autoboxing" and "Autounboxing" ---------------------------------------------------

  implicit def byte2Byte(x: Byte)           = java.lang.Byte.valueOf(x)
  implicit def short2Short(x: Short)        = java.lang.Short.valueOf(x)
  implicit def char2Character(x: Char)      = java.lang.Character.valueOf(x)
  implicit def int2Integer(x: Int)          = java.lang.Integer.valueOf(x)
  implicit def long2Long(x: Long)           = java.lang.Long.valueOf(x)
  implicit def float2Float(x: Float)        = java.lang.Float.valueOf(x)
  implicit def double2Double(x: Double)     = java.lang.Double.valueOf(x)
  implicit def boolean2Boolean(x: Boolean)  = java.lang.Boolean.valueOf(x)
  
  // These next eight implicits exist solely to exclude AnyRef methods from the
  // eight implicits above so that primitives are not coerced to AnyRefs.  They
  // only create such conflict for AnyRef methods, so the methods on the java.lang
  // boxed types are unambiguously reachable.
  implicit def byte2ByteConflict(x: Byte)           = new AnyRef
  implicit def short2ShortConflict(x: Short)        = new AnyRef
  implicit def char2CharacterConflict(x: Char)      = new AnyRef
  implicit def int2IntegerConflict(x: Int)          = new AnyRef
  implicit def long2LongConflict(x: Long)           = new AnyRef
  implicit def float2FloatConflict(x: Float)        = new AnyRef
  implicit def double2DoubleConflict(x: Double)     = new AnyRef
  implicit def boolean2BooleanConflict(x: Boolean)  = new AnyRef
  
  implicit def Byte2byte(x: java.lang.Byte): Byte             = x.byteValue
  implicit def Short2short(x: java.lang.Short): Short         = x.shortValue
  implicit def Character2char(x: java.lang.Character): Char   = x.charValue
  implicit def Integer2int(x: java.lang.Integer): Int         = x.intValue
  implicit def Long2long(x: java.lang.Long): Long             = x.longValue
  implicit def Float2float(x: java.lang.Float): Float         = x.floatValue
  implicit def Double2double(x: java.lang.Double): Double     = x.doubleValue
  implicit def Boolean2boolean(x: java.lang.Boolean): Boolean = x.booleanValue

  // Strings and CharSequences --------------------------------------------------------------

  implicit def any2stringadd(x: Any) = new runtime.StringAdd(x)
  implicit def augmentString(x: String): StringOps = new StringOps(x)
  implicit def unaugmentString(x: StringOps): String = x.repr

  implicit def stringCanBuildFrom: CanBuildFrom[String, Char, String] = 
    new CanBuildFrom[String, Char, String] { 
      def apply(from: String) = apply()
      def apply() = mutable.StringBuilder.newBuilder
    }

  implicit def seqToCharSequence(xs: collection.IndexedSeq[Char]): CharSequence = new CharSequence {
    def length: Int = xs.length
    def charAt(index: Int): Char = xs(index)
    def subSequence(start: Int, end: Int): CharSequence = seqToCharSequence(xs.slice(start, end))
    override def toString: String = xs.mkString("")
  }

  implicit def arrayToCharSequence(xs: Array[Char]): CharSequence = new CharSequence {
    def length: Int = xs.length
    def charAt(index: Int): Char = xs(index)
    def subSequence(start: Int, end: Int): CharSequence = arrayToCharSequence(xs.slice(start, end))
    override def toString: String = xs.mkString("")
  }
  
  // Type Constraints --------------------------------------------------------------

  /**
   * An instance of `A <:< B` witnesses that `A` is a subtype of `B`.
   * Requiring an implicit argument of the type `A <:< B` encodes
   * the generalized constraint `A <: B`.
   *
   * @note we need a new type constructor `<:<` and evidence `conforms`,
   * as reusing `Function1` and `identity` leads to ambiguities in
   * case of type errors (any2stringadd is inferred)
   *
   * To constrain any abstract type T that's in scope in a method's
   * argument list (not just the method's own type parameters) simply
   * add an implicit argument of type `T <:< U`, where U is the required
   * upper bound; or for lower-bounds, use: `L <:< T`, where L is the
   * required lower bound.
   *
   * In part contributed by Jason Zaugg.
   */
  @implicitNotFound(msg = "Cannot prove that ${From} <:< ${To}.")
  sealed abstract class <:<[-From, +To] extends (From => To) with Serializable
  private[this] final val singleton_<:< = new <:<[Any,Any] { def apply(x: Any): Any = x }
  // not in the <:< companion object because it is also
  // intended to subsume identity (which is no longer implicit)
  implicit def conforms[A]: A <:< A = singleton_<:<.asInstanceOf[A <:< A]

  /** An instance of `A =:= B` witnesses that the types `A` and `B` are equal.
   *
   * @see <:< for expressing subtyping constraints
   */
  @implicitNotFound(msg = "Cannot prove that ${From} =:= ${To}.")
  sealed abstract class =:=[From, To] extends (From => To) with Serializable
  private[this] final val singleton_=:= = new =:=[Any,Any] { def apply(x: Any): Any = x }
  object =:= {
     implicit def tpEquals[A]: A =:= A = singleton_=:=.asInstanceOf[A =:= A]
  }

  // less useful due to #2781
  @deprecated("Use From => To instead", "2.9.0")
  sealed abstract class <%<[-From, +To] extends (From => To) with Serializable
  object <%< {
    implicit def conformsOrViewsAs[A <% B, B]: A <%< B = new (A <%< B) {def apply(x: A) = x}
  }
 
  /** A type for which there is always an implicit value.
   *  @see fallbackCanBuildFrom in Array.scala
   */
  class DummyImplicit
  
  object DummyImplicit {
  
    /** An implicit value yielding a DummyImplicit.
     *   @see fallbackCanBuildFrom in Array.scala
     */
    implicit def dummyImplicit: DummyImplicit = new DummyImplicit
  }
}