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/* __ *\
** ________ ___ / / ___ 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 `Predef` object provides definitions that are accessible in all Scala
* compilation units without explicit qualification.
*
* === Commonly Used Types ===
* Predef provides type aliases for types which are commonly used, such as
* the immutable collection types [[scala.collection.immutable.Map]],
* [[scala.collection.immutable.Set]], and the [[scala.collection.immutable.List]]
* constructors ([[scala.collection.immutable.::]] and
* [[scala.collection.immutable.Nil]]).
* The types `Pair` (a [[scala.Tuple2]]) and `Triple` (a [[scala.Tuple3]]), with
* simple constructors, are also provided.
*
* === Console I/O ===
* Predef provides a number of simple functions for console I/O, such as
* `print`, `println`, `readLine`, `readInt`, etc. These functions are all
* aliases of the functions provided by [[scala.Console]].
*
* === Assertions ===
*
* A set of `assert` functions are provided for use as a way to document
* and dynamically check invariants in code. `assert` statements can be elided
* at runtime by providing the command line argument `-Xdisable-assertions` to
* the `scala` command.
*
* Variants of `assert` intended for use with static analysis tools are also
* provided: `assume`, `require` and `ensuring`. `require` and `ensuring` are
* intended for use as a means of design-by-contract style specification
* of pre- and post-conditions on functions, with the intention that these
* specifications could be consumed by a static analysis tool. For instance,
*
* {{{
* def addNaturals(nats: List[Int]): Int = {
* require(nats forall (_ >= 0), "List contains negative numbers")
* nats.foldLeft(0)(_ + _)
* } ensuring(_ >= 0)
* }}}
*
* The declaration of `addNaturals` states that the list of integers passed should
* only contain natural numbers (i.e. non-negative), and that the result returned
* will also be natural. `require` is distinct from `assert` in that if the
* condition fails, then the caller of the function is to blame rather than a
* logical error having been made within `addNaturals` itself. `ensures` is a
* form of `assert` that declares the guarantee the function is providing with
* regards to it's return value.
*
* === Implicit Conversions ===
* A number of commonly applied implicit conversions are also defined here, and
* in the parent type [[scala.LowPriorityImplicits]]. Implicit conversions
* are provided for the "widening" of numeric values, for instance, converting a
* Short value to a Long value as required, and to add additional higher-order
* functions to Array values. These are described in more detail in the documentation of [[scala.Array]].
*/
object Predef extends LowPriorityImplicits {
/**
* Retrieve the runtime representation of a class type. `classOf[T]` is equivalent to
* the class literal `T.class` in Java.
*
* @example {{{
* val listClass = classOf[List[_]]
* // listClass is java.lang.Class[List[_]] = class scala.collection.immutable.List
*
* val mapIntString = classOf[Map[Int,String]]
* // mapIntString is java.lang.Class[Map[Int,String]] = interface scala.collection.immutable.Map
* }}}
*/
def classOf[T]: Class[T] = null // This is a stub method. The actual implementation is filled in by the compiler.
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
@inline def implicitly[T](implicit e: T) = e // for summoning implicit values from the nether world -- TODO: when dependent method types are on by default, give this result type `e.type`, so that inliner has better chance of knowing which method to inline in calls like `implicitly[MatchingStrategy[Option]].zero`
@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 __resultOfEnsuring: A) {
// `__resultOfEnsuring` must be a public val to allow inlining.
// See comments in ArrowAssoc for more.
@deprecated("Use __resultOfEnsuring instead", "2.10.0")
def x = __resultOfEnsuring
def ensuring(cond: Boolean): A = { assert(cond); __resultOfEnsuring }
def ensuring(cond: Boolean, msg: => Any): A = { assert(cond, msg); __resultOfEnsuring }
def ensuring(cond: A => Boolean): A = { assert(cond(__resultOfEnsuring)); __resultOfEnsuring }
def ensuring(cond: A => Boolean, msg: => Any): A = { assert(cond(__resultOfEnsuring), msg); __resultOfEnsuring }
}
implicit def any2Ensuring[A](x: A): Ensuring[A] = new Ensuring(x)
/** `???` can be used for marking methods that remain to be implemented.
* @throws A `NotImplementedError`
*/
def ??? : Nothing = throw new NotImplementedError
// 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 __leftOfArrow: A) {
// `__leftOfArrow` must be a public val to allow inlining. The val
// used to be called `x`, but now goes by `__leftOfArrow`, as that
// reduces the chances of a user's writing `foo.__leftOfArrow` and
// being confused why they get an ambiguous implicit conversion
// error. (`foo.x` used to produce this error since both
// any2Ensuring and any2ArrowAssoc pimped an `x` onto everything)
@deprecated("Use __leftOfArrow instead", "2.10.0")
def x = __leftOfArrow
@inline def -> [B](y: B): Tuple2[A, B] = Tuple2(__leftOfArrow, 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 collection.AbstractTraversable[(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 collection.AbstractTraversable[(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
}
}
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