scala

# Predef

#### object Predef extends LowPriorityImplicits with DeprecatedPredef

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).

##### 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.

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`.

   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`.

   Annotations
     @implicitNotFound( msg = ... )
   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.

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.

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

   Annotations
     @implicitNotFound( msg = ... )
   See also

     `<:<` for expressing subtyping constraints

3. #### implicit final class ArrayCharSequence extends CharSequence

4. #### implicit final class ArrowAssoc[A] extends AnyVal

5. #### type Class[T] = java.lang.Class[T]

6. #### class DummyImplicit extends AnyRef

   A type for which there is always an implicit value.

   A type for which there is always an implicit value.

   See also

     scala.Array$, method `fallbackCanBuildFrom`

7. #### implicit final class Ensuring[A] extends AnyVal

8. #### type Function[-A, +B] = (A) ⇒ B

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

   Annotations
     @implicitNotFound( msg = "No Manifest available for ${T}." )

10. #### type Map[A, +B] = collection.immutable.Map[A, B]

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

12. #### implicit final class RichException extends AnyVal

13. #### implicit final class SeqCharSequence extends CharSequence

14. #### type Set[A] = collection.immutable.Set[A]

15. #### type String = java.lang.String

16. #### implicit final class StringFormat[A] extends AnyVal

17. #### implicit final class any2stringadd[A] extends AnyVal

18. #### type ClassManifest[T] = ClassTag[T]

    Annotations
      @implicitNotFound( msg = ... ) @deprecated
    Deprecated

      (Since version 2.10.0) Use `scala.reflect.ClassTag` instead

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

    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use built-in tuple syntax or Tuple2 instead

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

    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use built-in tuple syntax or Tuple3 instead

### Value Members

1. #### final def !=(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

2. #### final def ##(): Int

   Definition Classes
     AnyRef → Any

3. #### implicit def $conforms[A]: <:<[A, A]

4. #### object =:= extends Serializable

5. #### final def ==(arg0: Any): Boolean

   Definition Classes
     AnyRef → Any

6. #### def ???: Nothing

   `???` can be used for marking methods that remain to be implemented.

   `???` can be used for marking methods that remain to be implemented.

   Exceptions thrown
     A

     `NotImplementedError`

7. #### implicit def Boolean2boolean(x: java.lang.Boolean): Boolean

8. #### implicit def Byte2byte(x: java.lang.Byte): Byte

9. #### implicit def Character2char(x: Character): Char

10. #### implicit def Double2double(x: java.lang.Double): Double

11. #### object DummyImplicit

12. #### implicit def Float2float(x: java.lang.Float): Float

13. #### implicit def Integer2int(x: Integer): Int

14. #### implicit def Long2long(x: java.lang.Long): Long

15. #### val Manifest: ManifestFactory.type

16. #### val Map: collection.immutable.Map.type

17. #### val NoManifest: reflect.NoManifest.type

18. #### val Set: collection.immutable.Set.type

19. #### implicit def Short2short(x: java.lang.Short): Short

20. #### implicit val StringCanBuildFrom: CanBuildFrom[String, Char, String]

21. #### final def asInstanceOf[T0]: T0

    Definition Classes
      Any

22. #### 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`.

    assertion

      the expression to test

    message

      a String to include in the failure message

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

      elidable

23. #### 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`.

    assertion

      the expression to test

    Annotations
      @elidable( level = ASSERTION )
    See also

      elidable

24. #### 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`.

    assumption

      the expression to test

    message

      a String to include in the failure message

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

      elidable

25. #### 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`.

    assumption

      the expression to test

    Annotations
      @elidable( level = ASSERTION )
    See also

      elidable

26. #### implicit def augmentString(x: String): StringOps

    Annotations
      @inline()

27. #### implicit def boolean2Boolean(x: Boolean): java.lang.Boolean

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

29. #### implicit def booleanWrapper(x: Boolean): RichBoolean

    Definition Classes
      LowPriorityImplicits
    Annotations
      @inline()

30. #### implicit def byte2Byte(x: Byte): java.lang.Byte

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

32. #### implicit def byteWrapper(x: Byte): RichByte

    We prefer the java.lang.* boxed types to these wrappers in any potential conflicts.

    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.

    Note - these are inlined because they are value classes, but the call to xxxWrapper is not eliminated even though it does nothing. Even inlined, every call site does a no-op retrieval of Predef's MODULE$ because maybe loading Predef has side effects!

    Definition Classes
      LowPriorityImplicits
    Annotations
      @inline()

33. #### implicit def char2Character(x: Char): Character

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

35. #### implicit def charWrapper(c: Char): RichChar

    Definition Classes
      LowPriorityImplicits
    Annotations
      @inline()

36. #### 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

37. #### def clone(): AnyRef

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

38. #### implicit def double2Double(x: Double): java.lang.Double

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

40. #### implicit def doubleWrapper(x: Double): RichDouble

    Definition Classes
      LowPriorityImplicits
    Annotations
      @inline()

41. #### final def eq(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

42. #### def equals(arg0: Any): Boolean

    Definition Classes
      AnyRef → Any

43. #### implicit def fallbackStringCanBuildFrom[T]: CanBuildFrom[String, T, collection.immutable.IndexedSeq[T]]

    Definition Classes
      LowPriorityImplicits

44. #### def finalize(): Unit

    Attributes
      protected[java.lang]
    Definition Classes
      AnyRef
    Annotations
      @throws( classOf[java.lang.Throwable] )

45. #### implicit def float2Float(x: Float): java.lang.Float

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

47. #### implicit def floatWrapper(x: Float): RichFloat

    Definition Classes
      LowPriorityImplicits
    Annotations
      @inline()

48. #### implicit def genericArrayOps[T](xs: Array[T]): ArrayOps[T]

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

    Definition Classes
      LowPriorityImplicits

50. #### final def getClass(): java.lang.Class[_]

    Definition Classes
      AnyRef → Any

51. #### def hashCode(): Int

    Definition Classes
      AnyRef → Any

52. #### def identity[A](x: A): A

53. #### def implicitly[T](implicit e: T): T

    Annotations
      @inline()

54. #### implicit def int2Integer(x: Int): Integer

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

56. #### implicit def intWrapper(x: Int): RichInt

    Definition Classes
      LowPriorityImplicits
    Annotations
      @inline()

57. #### final def isInstanceOf[T0]: Boolean

    Definition Classes
      Any

58. #### def locally[T](x: T): T

    Annotations
      @inline()

59. #### implicit def long2Long(x: Long): java.lang.Long

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

61. #### implicit def longWrapper(x: Long): RichLong

    Definition Classes
      LowPriorityImplicits
    Annotations
      @inline()

62. #### def manifest[T](implicit m: Manifest[T]): Manifest[T]

63. #### final def ne(arg0: AnyRef): Boolean

    Definition Classes
      AnyRef

64. #### final def notify(): Unit

    Definition Classes
      AnyRef

65. #### final def notifyAll(): Unit

    Definition Classes
      AnyRef

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

67. #### def print(x: Any): Unit

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

69. #### def println(x: Any): Unit

70. #### def println(): Unit

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

72. #### 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.

    requirement

      the expression to test

    message

      a String to include in the failure message

    Annotations
      @inline()

73. #### 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.

    requirement

      the expression to test

74. #### implicit def short2Short(x: Short): java.lang.Short

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

76. #### implicit def shortWrapper(x: Short): RichShort

    Definition Classes
      LowPriorityImplicits
    Annotations
      @inline()

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

    Definition Classes
      AnyRef

78. #### def toString(): java.lang.String

    Definition Classes
      AnyRef → Any

79. #### implicit def tuple2ToZippedOps[T1, T2](x: (T1, T2)): Ops[T1, T2]

80. #### implicit def tuple3ToZippedOps[T1, T2, T3](x: (T1, T2, T3)): Ops[T1, T2, T3]

81. #### implicit def unaugmentString(x: StringOps): String

    Annotations
      @inline()

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

83. #### implicit def unwrapString(ws: WrappedString): String

    Definition Classes
      LowPriorityImplicits

84. #### final def wait(): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

85. #### final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

86. #### final def wait(arg0: Long): Unit

    Definition Classes
      AnyRef
    Annotations
      @throws( ... )

87. #### implicit def wrapBooleanArray(xs: Array[Boolean]): WrappedArray[Boolean]

    Definition Classes
      LowPriorityImplicits

88. #### implicit def wrapByteArray(xs: Array[Byte]): WrappedArray[Byte]

    Definition Classes
      LowPriorityImplicits

89. #### implicit def wrapCharArray(xs: Array[Char]): WrappedArray[Char]

    Definition Classes
      LowPriorityImplicits

90. #### implicit def wrapDoubleArray(xs: Array[Double]): WrappedArray[Double]

    Definition Classes
      LowPriorityImplicits

91. #### implicit def wrapFloatArray(xs: Array[Float]): WrappedArray[Float]

    Definition Classes
      LowPriorityImplicits

92. #### implicit def wrapIntArray(xs: Array[Int]): WrappedArray[Int]

    Definition Classes
      LowPriorityImplicits

93. #### implicit def wrapLongArray(xs: Array[Long]): WrappedArray[Long]

    Definition Classes
      LowPriorityImplicits

94. #### implicit def wrapRefArray[T <: AnyRef](xs: Array[T]): WrappedArray[T]

    Definition Classes
      LowPriorityImplicits

95. #### implicit def wrapShortArray(xs: Array[Short]): WrappedArray[Short]

    Definition Classes
      LowPriorityImplicits

96. #### implicit def wrapString(s: String): WrappedString

    Definition Classes
      LowPriorityImplicits

97. #### implicit def wrapUnitArray(xs: Array[Unit]): WrappedArray[Unit]

    Definition Classes
      LowPriorityImplicits

### Deprecated Value Members

1. #### val ClassManifest: ClassManifestFactory.type

   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use `scala.reflect.ClassTag` instead

2. #### object Pair

   Annotations
     @deprecated
   Deprecated

     (Since version 2.11.0) Use built-in tuple syntax or Tuple2 instead

3. #### object Triple

   Annotations
     @deprecated
   Deprecated

     (Since version 2.11.0) Use built-in tuple syntax or Tuple3 instead

4. #### def any2ArrowAssoc[A](x: A): ArrowAssoc[A]

   Definition Classes
     DeprecatedPredef
   Annotations
     @deprecated
   Deprecated

     (Since version 2.11.0) Use `ArrowAssoc`

5. #### def any2Ensuring[A](x: A): Ensuring[A]

   Definition Classes
     DeprecatedPredef
   Annotations
     @deprecated
   Deprecated

     (Since version 2.11.0) Use `Ensuring`

6. #### def any2stringfmt(x: Any): StringFormat[Any]

   Definition Classes
     DeprecatedPredef
   Annotations
     @deprecated
   Deprecated

     (Since version 2.11.0) Use `StringFormat`

7. #### def arrayToCharSequence(xs: Array[Char]): CharSequence

   Definition Classes
     DeprecatedPredef
   Annotations
     @deprecated
   Deprecated

     (Since version 2.11.0) Use `ArrayCharSequence`

8. #### def classManifest[T](implicit m: ClassManifest[T]): ClassManifest[T]

   Annotations
     @deprecated
   Deprecated

     (Since version 2.10.0) Use scala.reflect.classTag[T] instead

9. #### def conforms[A]: <:<[A, A]

   Annotations
     @deprecated
   Deprecated

     (Since version 2.11.0) Use `implicitly[T <:< U]` or `identity` instead.

10. #### def error(message: String): Nothing

    Annotations
      @deprecated
    Deprecated

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

11. #### def exceptionWrapper(exc: Throwable): RichException

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use `Throwable` directly

12. #### def readBoolean(): Boolean

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

13. #### def readByte(): Byte

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

14. #### def readChar(): Char

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

15. #### def readDouble(): Double

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

16. #### def readFloat(): Float

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

17. #### def readInt(): Int

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

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

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

19. #### def readLine(): String

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

20. #### def readLong(): Long

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

21. #### def readShort(): Short

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

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

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

23. #### def readf1(format: String): Any

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

24. #### def readf2(format: String): (Any, Any)

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

25. #### def readf3(format: String): (Any, Any, Any)

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use the method in `scala.io.StdIn`

26. #### def seqToCharSequence(xs: collection.IndexedSeq[Char]): CharSequence

    Definition Classes
      DeprecatedPredef
    Annotations
      @deprecated
    Deprecated

      (Since version 2.11.0) Use `SeqCharSequence`

### Inherited from DeprecatedPredef

### Inherited from LowPriorityImplicits

### Inherited from AnyRef

### Inherited from Any

### Ungrouped