scala

Predef

object Predef extends LowPriorityImplicits

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 Map, Set, and the List constructors (scala.collection.immutable.:: and scala.collection.immutable.Nil). The types Pair (a Tuple2) and Triple (a 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 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 Array.

Source
Predef.scala
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Type Members

  1. sealed abstract class <:<[-From, +To] extends (From) ⇒ To with Serializable

    An instance of A <:< B witnesses that A is a subtype of B.

  2. sealed abstract class =:=[From, To] extends (From) ⇒ To with Serializable

    An instance of A =:= B witnesses that the types A and B are equal.

  3. final class ArrowAssoc[A] extends AnyRef

  4. type Class[T] = Class[T]

  5. type ClassManifest[T] = ClassManifest[T]

  6. class DummyImplicit extends AnyRef

    A type for which there is always an implicit value.

  7. final class Ensuring[A] extends AnyRef

  8. type Function[-A, +B] = (A) ⇒ B

  9. type Manifest[T] = Manifest[T]

  10. type Map[A, +B] = Map[A, B]

  11. type OptManifest[T] = OptManifest[T]

  12. type Pair[+A, +B] = (A, B)

  13. type Set[A] = Set[A]

  14. type String = String

  15. type Triple[+A, +B, +C] = (A, B, C)

  16. sealed abstract class <%<[-From, +To] extends (From) ⇒ To with Serializable

    Annotations
    @deprecated
    Deprecated

    (Since version 2.9.0) Use From => To instead

Value Members

  1. final def !=(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef
  2. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

    true if !(this == that), false otherwise.

    Definition Classes
    Any
  3. final def ##(): Int

    Equivalent to x.hashCode except for boxed numeric types.

    Equivalent to x.hashCode except for boxed numeric types. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them.

    returns

    a hash value consistent with ==

    Definition Classes
    AnyRef → Any
  4. val $scope: xml.TopScope.type

  5. object <%< extends Serializable

  6. object =:= extends Serializable

  7. final def ==(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef
  8. final def ==(arg0: Any): Boolean

    Test two objects for equality.

    Test two objects for equality.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    Definition Classes
    Any
  9. val AnyRef: SpecializableCompanion

  10. implicit def Boolean2boolean(x: Boolean): Boolean

  11. implicit def Boolean2booleanNullConflict(x: Null): Boolean

    Definition Classes
    LowPriorityImplicits
  12. implicit def Byte2byte(x: Byte): Byte

  13. implicit def Byte2byteNullConflict(x: Null): Byte

    Definition Classes
    LowPriorityImplicits
  14. implicit def Character2char(x: Character): Char

  15. implicit def Character2charNullConflict(x: Null): Char

    Definition Classes
    LowPriorityImplicits
  16. val ClassManifest: reflect.ClassManifest.type

  17. implicit def Double2double(x: Double): Double

  18. implicit def Double2doubleNullConflict(x: Null): Double

    Definition Classes
    LowPriorityImplicits
  19. object DummyImplicit extends AnyRef

  20. implicit def Float2float(x: Float): Float

  21. implicit def Float2floatNullConflict(x: Null): Float

    Definition Classes
    LowPriorityImplicits
  22. implicit def Integer2int(x: Integer): Int

  23. implicit def Integer2intNullConflict(x: Null): Int

    Definition Classes
    LowPriorityImplicits
  24. implicit def Long2long(x: Long): Long

  25. implicit def Long2longNullConflict(x: Null): Long

    Definition Classes
    LowPriorityImplicits
  26. val Manifest: reflect.Manifest.type

  27. val Map: scala.collection.immutable.Map.type

  28. val NoManifest: reflect.NoManifest.type

  29. object Pair extends Serializable

  30. val Set: scala.collection.immutable.Set.type

  31. implicit def Short2short(x: Short): Short

  32. implicit def Short2shortNullConflict(x: Null): Short

    Definition Classes
    LowPriorityImplicits
  33. object Triple extends Serializable

  34. implicit def any2ArrowAssoc[A](x: A): ArrowAssoc[A]

  35. implicit def any2Ensuring[A](x: A): Ensuring[A]

  36. implicit def any2stringadd(x: Any): StringAdd

  37. implicit def arrayToCharSequence(xs: Array[Char]): CharSequence

  38. final def asInstanceOf[T0]: T0

    Cast the receiver object to be of type T0.

    Cast the receiver object to be of type T0.

    Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

    returns

    the receiver object.

    Definition Classes
    Any
    Exceptions thrown
    ClassCastException

    if the receiver object is not an instance of the erasure of type T0.

  39. final def assert(assertion: Boolean, message: ⇒ Any): Unit

    Tests an expression, throwing an AssertionError if false.

    Tests an expression, throwing an AssertionError if false. Calls to this method will not be generated if -Xelide-below is at least ASSERTION.

    Annotations
    @elidable( level = ASSERTION ) @inline()
    See also

    elidable

  40. def assert(assertion: Boolean): Unit

    Tests an expression, throwing an AssertionError if false.

    Tests an expression, throwing an AssertionError if false. Calls to this method will not be generated if -Xelide-below is at least ASSERTION.

    Annotations
    @elidable( level = ASSERTION )
    See also

    elidable

  41. final def assume(assumption: Boolean, message: ⇒ Any): Unit

    Tests an expression, throwing an AssertionError if false.

    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.

    Annotations
    @elidable( level = ASSERTION ) @inline()
    See also

    elidable

  42. def assume(assumption: Boolean): Unit

    Tests an expression, throwing an AssertionError if false.

    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.

    Annotations
    @elidable( level = ASSERTION )
    See also

    elidable

  43. implicit def augmentString(x: String): StringOps

  44. implicit def boolean2Boolean(x: Boolean): Boolean

  45. implicit def boolean2BooleanConflict(x: Boolean): AnyRef

  46. implicit def booleanArrayOps(xs: Array[Boolean]): ArrayOps[Boolean]

  47. implicit def booleanWrapper(x: Boolean): RichBoolean

    Definition Classes
    LowPriorityImplicits
  48. implicit def byte2Byte(x: Byte): Byte

  49. implicit def byte2ByteConflict(x: Byte): AnyRef

  50. implicit def byte2double(x: Byte): Double

  51. implicit def byte2float(x: Byte): Float

  52. implicit def byte2int(x: Byte): Int

  53. implicit def byte2long(x: Byte): Long

  54. implicit def byte2short(x: Byte): Short

  55. implicit def byteArrayOps(xs: Array[Byte]): ArrayOps[Byte]

  56. implicit def byteWrapper(x: Byte): RichByte

    We prefer the java.

    We prefer the java.lang.* boxed types to these wrappers in any potential conflicts. Conflicts do exist because the wrappers need to implement ScalaNumber in order to have a symmetric equals method, but that implies implementing java.lang.Number as well.

    Definition Classes
    LowPriorityImplicits
  57. implicit def char2Character(x: Char): Character

  58. implicit def char2CharacterConflict(x: Char): AnyRef

  59. implicit def char2double(x: Char): Double

  60. implicit def char2float(x: Char): Float

  61. implicit def char2int(x: Char): Int

  62. implicit def char2long(x: Char): Long

  63. implicit def charArrayOps(xs: Array[Char]): ArrayOps[Char]

  64. implicit def charWrapper(c: Char): RichChar

    Definition Classes
    LowPriorityImplicits
  65. def classManifest[T](implicit m: ClassManifest[T]): ClassManifest[T]

  66. def classOf[T]: Class[T]

    Retrieve the runtime representation of a class type.

    Retrieve the runtime representation of a class type. classOf[T] is equivalent to the class literal T.class in Java.

    Example:
    1. 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
      
  67. def clone(): AnyRef

    Create a copy of the receiver object.

    Create a copy of the receiver object.

    The default implementation of the clone method is platform dependent.

    returns

    a copy of the receiver object.

    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  68. implicit def conforms[A]: <:<[A, A]

  69. implicit def double2Double(x: Double): Double

  70. implicit def double2DoubleConflict(x: Double): AnyRef

  71. implicit def doubleArrayOps(xs: Array[Double]): ArrayOps[Double]

  72. implicit def doubleWrapper(x: Double): RichDouble

    Definition Classes
    LowPriorityImplicits
  73. final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (arg0) is a reference to the receiver object (this).

    Tests whether the argument (arg0) is a reference to the receiver object (this).

    The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    • It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.
    • For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
    • null.eq(null) returns true.

    When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

    returns

    true if the argument is a reference to the receiver object; false otherwise.

    Definition Classes
    AnyRef
  74. def equals(arg0: Any): Boolean

    The equality method for reference types.

    The equality method for reference types. See equals in Any.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    Definition Classes
    AnyRef → Any
  75. implicit def exceptionWrapper(exc: Throwable): RichException

  76. implicit def fallbackStringCanBuildFrom[T]: CanBuildFrom[String, T, IndexedSeq[T]]

    Definition Classes
    LowPriorityImplicits
  77. def finalize(): Unit

    Called by the garbage collector on the receiver object when there are no more references to the object.

    Called by the garbage collector on the receiver object when there are no more references to the object.

    The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

    Attributes
    protected[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  78. implicit def float2Float(x: Float): Float

  79. implicit def float2FloatConflict(x: Float): AnyRef

  80. implicit def float2double(x: Float): Double

  81. implicit def floatArrayOps(xs: Array[Float]): ArrayOps[Float]

  82. implicit def floatWrapper(x: Float): RichFloat

    Definition Classes
    LowPriorityImplicits
  83. implicit def genericArrayOps[T](xs: Array[T]): ArrayOps[T]

  84. implicit def genericWrapArray[T](xs: Array[T]): WrappedArray[T]

    Definition Classes
    LowPriorityImplicits
  85. final def getClass(): java.lang.Class[_]

    A representation that corresponds to the dynamic class of the receiver object.

    A representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

    a representation that corresponds to the dynamic class of the receiver object.

    Definition Classes
    AnyRef → Any
    Note

    not specified by SLS as a member of AnyRef

  86. def hashCode(): Int

    The hashCode method for reference types.

    The hashCode method for reference types. See hashCode in Any.

    returns

    the hash code value for this object.

    Definition Classes
    AnyRef → Any
  87. def identity[A](x: A): A

  88. def implicitly[T](implicit e: T): T

  89. implicit def int2Integer(x: Int): Integer

  90. implicit def int2IntegerConflict(x: Int): AnyRef

  91. implicit def int2double(x: Int): Double

  92. implicit def int2float(x: Int): Float

  93. implicit def int2long(x: Int): Long

  94. implicit def intArrayOps(xs: Array[Int]): ArrayOps[Int]

  95. implicit def intWrapper(x: Int): RichInt

    Definition Classes
    LowPriorityImplicits
  96. final def isInstanceOf[T0]: Boolean

    Test whether the dynamic type of the receiver object is T0.

    Test whether the dynamic type of the receiver object is T0.

    Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

    returns

    true if the receiver object is an instance of erasure of type T0; false otherwise.

    Definition Classes
    Any
  97. def locally[T](x: T): T

    Annotations
    @inline()
  98. implicit def long2Long(x: Long): Long

  99. implicit def long2LongConflict(x: Long): AnyRef

  100. implicit def long2double(x: Long): Double

  101. implicit def long2float(x: Long): Float

  102. implicit def longArrayOps(xs: Array[Long]): ArrayOps[Long]

  103. implicit def longWrapper(x: Long): RichLong

    Definition Classes
    LowPriorityImplicits
  104. def manifest[T](implicit m: Manifest[T]): Manifest[T]

  105. final def ne(arg0: AnyRef): Boolean

    Equivalent to !(this eq that).

    Equivalent to !(this eq that).

    returns

    true if the argument is not a reference to the receiver object; false otherwise.

    Definition Classes
    AnyRef
  106. final def notify(): Unit

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  107. final def notifyAll(): Unit

    Wakes up all threads that are waiting on the receiver object's monitor.

    Wakes up all threads that are waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  108. def optManifest[T](implicit m: OptManifest[T]): OptManifest[T]

  109. def print(x: Any): Unit

  110. def printf(text: String, xs: Any*): Unit

  111. def println(x: Any): Unit

  112. def println(): Unit

  113. def readBoolean(): Boolean

  114. def readByte(): Byte

  115. def readChar(): Char

  116. def readDouble(): Double

  117. def readFloat(): Float

  118. def readInt(): Int

  119. def readLine(text: String, args: Any*): String

  120. def readLine(): String

  121. def readLong(): Long

  122. def readShort(): Short

  123. def readf(format: String): List[Any]

  124. def readf1(format: String): Any

  125. def readf2(format: String): (Any, Any)

  126. def readf3(format: String): (Any, Any, Any)

  127. implicit def refArrayOps[T <: AnyRef](xs: Array[T]): ArrayOps[T]

  128. final def require(requirement: Boolean, message: ⇒ Any): Unit

    Tests an expression, throwing an IllegalArgumentException if false.

    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.

    Annotations
    @inline()
  129. def require(requirement: Boolean): Unit

    Tests an expression, throwing an IllegalArgumentException if false.

    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.

  130. implicit def seqToCharSequence(xs: IndexedSeq[Char]): CharSequence

  131. implicit def short2Short(x: Short): Short

  132. implicit def short2ShortConflict(x: Short): AnyRef

  133. implicit def short2double(x: Short): Double

  134. implicit def short2float(x: Short): Float

  135. implicit def short2int(x: Short): Int

  136. implicit def short2long(x: Short): Long

  137. implicit def shortArrayOps(xs: Array[Short]): ArrayOps[Short]

  138. implicit def shortWrapper(x: Short): RichShort

    Definition Classes
    LowPriorityImplicits
  139. implicit def stringCanBuildFrom: CanBuildFrom[String, Char, String]

  140. final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
    AnyRef
  141. def toString(): String

    Creates a String representation of this object.

    Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

    returns

    a String representation of the object.

    Definition Classes
    AnyRef → Any
  142. implicit def unaugmentString(x: StringOps): String

  143. implicit def unitArrayOps(xs: Array[Unit]): ArrayOps[Unit]

  144. implicit def unwrapString(ws: WrappedString): String

    Definition Classes
    LowPriorityImplicits
  145. final def wait(): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()
  146. final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()
  147. final def wait(arg0: Long): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()
  148. implicit def wrapBooleanArray(xs: Array[Boolean]): WrappedArray[Boolean]

    Definition Classes
    LowPriorityImplicits
  149. implicit def wrapByteArray(xs: Array[Byte]): WrappedArray[Byte]

    Definition Classes
    LowPriorityImplicits
  150. implicit def wrapCharArray(xs: Array[Char]): WrappedArray[Char]

    Definition Classes
    LowPriorityImplicits
  151. implicit def wrapDoubleArray(xs: Array[Double]): WrappedArray[Double]

    Definition Classes
    LowPriorityImplicits
  152. implicit def wrapFloatArray(xs: Array[Float]): WrappedArray[Float]

    Definition Classes
    LowPriorityImplicits
  153. implicit def wrapIntArray(xs: Array[Int]): WrappedArray[Int]

    Definition Classes
    LowPriorityImplicits
  154. implicit def wrapLongArray(xs: Array[Long]): WrappedArray[Long]

    Definition Classes
    LowPriorityImplicits
  155. implicit def wrapRefArray[T <: AnyRef](xs: Array[T]): WrappedArray[T]

    Definition Classes
    LowPriorityImplicits
  156. implicit def wrapShortArray(xs: Array[Short]): WrappedArray[Short]

    Definition Classes
    LowPriorityImplicits
  157. implicit def wrapString(s: String): WrappedString

    Definition Classes
    LowPriorityImplicits
  158. implicit def wrapUnitArray(xs: Array[Unit]): WrappedArray[Unit]

    Definition Classes
    LowPriorityImplicits
  159. implicit def zipped2ToTraversable[El1, El2](zz: (_$1, _$2)#Zipped[_, El1, _, El2]): Traversable[(El1, El2)]

  160. implicit def zipped3ToTraversable[El1, El2, El3](zz: (_$5, _$6, _$7)#Zipped[_, El1, _, El2, _, El3]): Traversable[(El1, El2, El3)]

Deprecated Value Members

  1. def error(message: String): Nothing

    Annotations
    @deprecated
    Deprecated

    (Since version 2.9.0) Use sys.error(message) instead

  2. def exit(status: Int): Nothing

    Annotations
    @deprecated
    Deprecated

    (Since version 2.9.0) Use sys.exit(status) instead

  3. def exit(): Nothing

    Annotations
    @deprecated
    Deprecated

    (Since version 2.9.0) Use sys.exit() instead

  4. def format(text: String, xs: Any*): String

    Annotations
    @deprecated
    Deprecated

    (Since version 2.9.0) Use formatString.format(args: _*) or arg.formatted(formatString) instead

Inherited from LowPriorityImplicits

Inherited from AnyRef

Inherited from Any