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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LowPriorityImplicits, AnyRef, Any
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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