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 scala.collection.immutable.Map and scala.collection.immutable.Set.

Console Output

For basic console output, Predef provides convenience methods print and println, which are aliases of the methods in the object scala.Console.

Assertions

A set of assert functions are provided for use as a way to document and dynamically check invariants in code. Invocations of assert can be elided at compile time by providing the command line option -Xdisable-assertions, which raises -Xelide-below above elidable.ASSERTION, to the scalac 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. ensuring is a form of assert that declares the guarantee the function is providing with regards to its 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

Linear Supertypes

LowPriorityImplicits, LowPriorityImplicits2, AnyRef, Any

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LowPriorityImplicits
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Type Members

final class ArrayCharSequence extends CharSequence
implicit final class ArrowAssoc[A] extends AnyVal
type Class[T] = java.lang.Class[T]
implicit final class Ensuring[A] extends AnyVal
type Function[-A, +B] = (A) => B
type Manifest[T] = reflect.Manifest[T]
Annotations
@implicitNotFound(msg = "No Manifest available for ${T}.")
type Map[K, +V] = collection.immutable.Map[K, V]
type OptManifest[T] = reflect.OptManifest[T]
final class SeqCharSequence extends CharSequence
type Set[A] = collection.immutable.Set[A]
type String = java.lang.String
The String type in Scala has all the methods of the underlying java.lang.String, of which it is just an alias.
The String type in Scala has all the methods of the underlying java.lang.String, of which it is just an alias. (See the documentation corresponding to your Java version, for example https://docs.oracle.com/javase/8/docs/api/java/lang/String.html.) In addition, extension methods in scala.collection.StringOps are added implicitly through the conversion augmentString.
implicit final class StringFormat[A] extends AnyVal

Deprecated Type Members

implicit final class any2stringadd[A] extends AnyVal
Injects String concatenation operator + to any classes.
Injects String concatenation operator + to any classes.
Annotations
@deprecated
Deprecated
(Since version 2.13.0) Implicit injection of + is deprecated. Convert to String to call +

Value Members

final def !=(arg0: Any): Boolean
Test two objects for inequality.
Test two objects for inequality.
returns
true if !(this == that), false otherwise.
Definition Classes
AnyRef → Any
final def ##: Int
Equivalent to x.hashCode except for boxed numeric types and null.
Equivalent to x.hashCode except for boxed numeric types and null. 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. For null returns a hashcode where null.hashCode throws a NullPointerException.
returns
a hash value consistent with ==
Definition Classes
AnyRef → Any
implicit def $conforms[A]: (A) => A
An implicit of type A => A is available for all A because it can always be implemented using the identity function.
An implicit of type A => A is available for all A because it can always be implemented using the identity function. This also means that an implicit of type A => B is always available when A <: B, because (A => A) <: (A => B).
val ->: Tuple2.type
Allows destructuring tuples with the same syntax as constructing them.
Allows destructuring tuples with the same syntax as constructing them.
Example:
1. val tup = "foobar" -> 3 val c = tup match { case str -> i => str.charAt(i) }
final def ==(arg0: Any): Boolean
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).
returns
true if the receiver object is equivalent to the argument; false otherwise.
Definition Classes
AnyRef → Any
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
NotImplementedError when ??? is invoked.
def ArrayCharSequence(arrayOfChars: Array[Char]): ArrayCharSequence
implicit def Boolean2boolean(x: java.lang.Boolean): Boolean
implicit def Byte2byte(x: java.lang.Byte): Byte
implicit def Character2char(x: Character): Char
implicit def Double2double(x: java.lang.Double): Double
implicit def Float2float(x: java.lang.Float): Float
implicit def Integer2int(x: Integer): Int
implicit def Long2long(x: java.lang.Long): Long
val Manifest: reflect.Manifest.type
val Map: collection.immutable.Map.type
val NoManifest: reflect.NoManifest.type
def SeqCharSequence(sequenceOfChars: collection.IndexedSeq[Char]): SeqCharSequence
val Set: collection.immutable.Set.type
implicit def Short2short(x: java.lang.Short): Short
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.
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 greater than ASSERTION.
assertion
the expression to test
message
a String to include in the failure message
Annotations
@elidable(level = ASSERTION) @inline()
See also
elidable
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 greater than ASSERTION.
assertion
the expression to test
Annotations
@elidable(level = ASSERTION)
See also
elidable
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 greater than ASSERTION.
assumption
the expression to test
message
a String to include in the failure message
Annotations
@elidable(level = ASSERTION) @inline()
See also
elidable
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 greater than ASSERTION.
assumption
the expression to test
Annotations
@elidable(level = ASSERTION)
See also
elidable
implicit def augmentString(x: String): StringOps
Annotations
@inline()
implicit def boolean2Boolean(x: Boolean): java.lang.Boolean
implicit def booleanArrayOps(xs: Array[Boolean]): ArrayOps[Boolean]
Annotations
@inline()
implicit def booleanWrapper(x: Boolean): RichBoolean
Definition Classes
LowPriorityImplicits
Annotations
@inline()
implicit def byte2Byte(x: Byte): java.lang.Byte
implicit def byteArrayOps(xs: Array[Byte]): ArrayOps[Byte]
Annotations
@inline()
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()
implicit def char2Character(x: Char): Character
implicit def charArrayOps(xs: Array[Char]): ArrayOps[Char]
Annotations
@inline()
implicit def charWrapper(c: Char): RichChar
Definition Classes
LowPriorityImplicits
Annotations
@inline()

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.

returns: The runtime Class representation of type T.

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 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(classOf[java.lang.CloneNotSupportedException]) @native()
Note
not specified by SLS as a member of AnyRef
implicit def double2Double(x: Double): java.lang.Double
implicit def doubleArrayOps(xs: Array[Double]): ArrayOps[Double]
Annotations
@inline()
implicit def doubleWrapper(x: Double): RichDouble
Definition Classes
LowPriorityImplicits
Annotations
@inline()
final def eq(arg0: AnyRef): Boolean
Tests whether the argument (that) is a reference to the receiver object (this).
Tests whether the argument (that) 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
def equals(arg0: AnyRef): Boolean
The equality method for reference types.
The equality method for reference types. Default implementation delegates to eq.
See also equals in scala.Any.
returns
true if the receiver object is equivalent to the argument; false otherwise.
Definition Classes
AnyRef → Any
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(classOf[java.lang.Throwable])
Note
not specified by SLS as a member of AnyRef
implicit def float2Float(x: Float): java.lang.Float
implicit def floatArrayOps(xs: Array[Float]): ArrayOps[Float]
Annotations
@inline()
implicit def floatWrapper(x: Float): RichFloat
Definition Classes
LowPriorityImplicits
Annotations
@inline()
implicit def genericArrayOps[T](xs: Array[T]): ArrayOps[T]
Annotations
@inline()
implicit def genericWrapArray[T](xs: Array[T]): ArraySeq[T]
Definition Classes
LowPriorityImplicits
final def getClass(): java.lang.Class[_ <: AnyRef]
Returns the runtime class representation of the object.
Returns the runtime class representation of the object.
returns
a class object corresponding to the runtime type of the receiver.
Definition Classes
AnyRef → Any
Annotations
@native()
def hashCode(): Int
The hashCode method for reference types.
The hashCode method for reference types. See hashCode in scala.Any.
returns
the hash code value for this object.
Definition Classes
AnyRef → Any
Annotations
@native()
def identity[A](x: A): A
A method that returns its input value.
A method that returns its input value.
A
type of the input value x.
x
the value of type A to be returned.
returns
the value x.
Annotations
@inline()
def implicitly[T](implicit e: T): T
Summon an implicit value of type T.
Summon an implicit value of type T. Usually, the argument is not passed explicitly.
T
the type of the value to be summoned
returns
the implicit value of type T
Annotations
@inline()
implicit def int2Integer(x: Int): Integer
implicit def intArrayOps(xs: Array[Int]): ArrayOps[Int]
Annotations
@inline()
implicit def intWrapper(x: Int): RichInt
Definition Classes
LowPriorityImplicits
Annotations
@inline()
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
def locally[T](x: T): T
Used to mark code blocks as being expressions, instead of being taken as part of anonymous classes and the like.
Used to mark code blocks as being expressions, instead of being taken as part of anonymous classes and the like. This is just a different name for identity.
Annotations
@inline()
Example:
1. Separating code blocks from new:
  val x = new AnyRef { val y = ... println(y) } // the { ... } block is seen as the body of an anonymous class val x = new AnyRef { val y = ... println(y) } // an empty line is a brittle "fix" val x = new AnyRef locally { val y = ... println(y) } // locally guards the block and helps communicate intent
implicit def long2Long(x: Long): java.lang.Long
implicit def longArrayOps(xs: Array[Long]): ArrayOps[Long]
Annotations
@inline()
implicit def longWrapper(x: Long): RichLong
Definition Classes
LowPriorityImplicits
Annotations
@inline()
def manifest[T](implicit m: Manifest[T]): Manifest[T]
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
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
Annotations
@native()
Note
not specified by SLS as a member of AnyRef
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
Annotations
@native()
Note
not specified by SLS as a member of AnyRef
def optManifest[T](implicit m: OptManifest[T]): OptManifest[T]
def print(x: Any): Unit
Prints an object to out using its toString method.
Prints an object to out using its toString method.
x
the object to print; may be null.
def printf(text: String, xs: Any*): Unit
Prints its arguments as a formatted string to the default output, based on a string pattern (in a fashion similar to printf in C).
Prints its arguments as a formatted string to the default output, based on a string pattern (in a fashion similar to printf in C).
The interpretation of the formatting patterns is described in java.util.Formatter.
Consider using the f interpolator as more type safe and idiomatic.
text
the pattern for formatting the arguments.
xs
the arguments used to instantiate the pattern.
Exceptions thrown
java.lang.IllegalArgumentException if there was a problem with the format string or arguments
See also
StringContext.f
def println(x: Any): Unit
Prints out an object to the default output, followed by a newline character.
Prints out an object to the default output, followed by a newline character.
x
the object to print.
def println(): Unit
Prints a newline character on the default output.
implicit def refArrayOps[T <: AnyRef](xs: Array[T]): ArrayOps[T]
Annotations
@inline()
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()
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
implicit def short2Short(x: Short): java.lang.Short
implicit def shortArrayOps(xs: Array[Short]): ArrayOps[Short]
Annotations
@inline()
implicit def shortWrapper(x: Short): RichShort
Definition Classes
LowPriorityImplicits
Annotations
@inline()
final def synchronized[T0](arg0: => T0): T0
Executes the code in body with an exclusive lock on this.
Executes the code in body with an exclusive lock on this.
returns
the result of body
Definition Classes
AnyRef
def toString(): java.lang.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
implicit def tuple2ToZippedOps[T1, T2](x: (T1, T2)): Ops[T1, T2]
implicit def tuple3ToZippedOps[T1, T2, T3](x: (T1, T2, T3)): Ops[T1, T2, T3]
implicit def unitArrayOps(xs: Array[Unit]): ArrayOps[Unit]
Annotations
@inline()
def valueOf[T](implicit vt: ValueOf[T]): T
Retrieve the single value of a type with a unique inhabitant.
Retrieve the single value of a type with a unique inhabitant.
Annotations
@inline()
Example:
1. object Foo val foo = valueOf[Foo.type] // foo is Foo.type = Foo val bar = valueOf[23] // bar is 23.type = 23
final def wait(): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait--.
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])
Note
not specified by SLS as a member of AnyRef
final def wait(arg0: Long, arg1: Int): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-int-
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])
Note
not specified by SLS as a member of AnyRef
final def wait(arg0: Long): Unit
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
See https://docs.oracle.com/javase/8/docs/api/java/lang/Object.html#wait-long-.
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()
Note
not specified by SLS as a member of AnyRef
implicit def wrapBooleanArray(xs: Array[Boolean]): ofBoolean
Definition Classes
LowPriorityImplicits
implicit def wrapByteArray(xs: Array[Byte]): ofByte
Definition Classes
LowPriorityImplicits
implicit def wrapCharArray(xs: Array[Char]): ofChar
Definition Classes
LowPriorityImplicits
implicit def wrapDoubleArray(xs: Array[Double]): ofDouble
Definition Classes
LowPriorityImplicits
implicit def wrapFloatArray(xs: Array[Float]): ofFloat
Definition Classes
LowPriorityImplicits
implicit def wrapIntArray(xs: Array[Int]): ofInt
Definition Classes
LowPriorityImplicits
implicit def wrapLongArray(xs: Array[Long]): ofLong
Definition Classes
LowPriorityImplicits
implicit def wrapRefArray[T <: AnyRef](xs: Array[T]): ofRef[T]
Definition Classes
LowPriorityImplicits
implicit def wrapShortArray(xs: Array[Short]): ofShort
Definition Classes
LowPriorityImplicits
implicit def wrapString(s: String): WrappedString
Definition Classes
LowPriorityImplicits
implicit def wrapUnitArray(xs: Array[Unit]): ofUnit
Definition Classes
LowPriorityImplicits

Deprecated Value Members

implicit def copyArrayToImmutableIndexedSeq[T](xs: Array[T]): IndexedSeq[T]
Definition Classes
LowPriorityImplicits2
Annotations
@deprecated
Deprecated
(Since version 2.13.0) Implicit conversions from Array to immutable.IndexedSeq are implemented by copying; Use the more efficient non-copying ArraySeq.unsafeWrapArray or an explicit toIndexedSeq call

Inherited from LowPriorityImplicits

Inherited from LowPriorityImplicits2

Inherited from AnyRef

Inherited from Any

Utility Methods

Assertions

These methods support program verification and runtime correctness.

Console Output

These methods provide output via the console.

Aliases

These aliases bring selected immutable types into scope without any imports.

String Conversions

Conversions from String to StringOps or WrappedString.

Implicit Classes

These implicit classes add useful extension methods to every type.

CharSequence Wrappers

Wrappers that implements CharSequence and were implicit classes.

Java to Scala

Implicit conversion from Java primitive wrapper types to Scala equivalents.

Scala to Java

Implicit conversion from Scala AnyVals to Java primitive wrapper types equivalents.

Array to ArraySeq

Conversions from Arrays to ArraySeqs.

Packages

Package structure

Automatic imports

Guide

Common Imports

Specifying Durations

Using Futures For Non-blocking Computation

Avoid Blocking

Predef

object Predef extends LowPriorityImplicits

Commonly Used Types

Console Output

Assertions

Implicit Conversions

Type Members

Deprecated Type Members

Value Members

Deprecated Value Members

Inherited from LowPriorityImplicits

Inherited from LowPriorityImplicits2

Inherited from AnyRef

Inherited from Any

Utility Methods

Assertions

Console Output

Aliases

String Conversions

Implicit Classes

CharSequence Wrappers

Java to Scala

Scala to Java

Array to ArraySeq

Ungrouped

Packages

Package structure

Automatic imports

Guide

Common Imports

Specifying Durations

Using Futures For Non-blocking Computation

Avoid Blocking

Predef

object Predef extends LowPriorityImplicits

Commonly Used Types

Console Output

Assertions

Implicit Conversions

Type Members

Deprecated Type Members

Value Members

Deprecated Value Members

Inherited from LowPriorityImplicits

Inherited from LowPriorityImplicits2

Inherited from AnyRef

Inherited from Any

Utility Methods

Assertions

Console Output

Aliases

String Conversions

Implicit Classes

CharSequence Wrappers

Java to Scala

Scala to Java

Array to ArraySeq

Ungrouped

Predef