final case class Left[+A, +B](value: A) extends Either[A, B] with Product with Serializable
The left side of the disjoint union, as opposed to the scala.util.Right side.
- Source
- Either.scala
- Alphabetic
- By Inheritance
- Left
- Either
- Serializable
- Product
- Equals
- AnyRef
- Any
- by MergeableEither
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
- Hide All
- Show All
- Public
- Protected
Instance Constructors
- new Left(value: A)
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 andnull
.Equivalent to
x.hashCode
except for boxed numeric types andnull
. 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. Fornull
returns a hashcode wherenull.hashCode
throws aNullPointerException
.- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
- def +(other: String): String
- Implicit
- This member is added by an implicit conversion from Left[A, B] toany2stringadd[Left[A, B]] performed by method any2stringadd in scala.Predef.
- Definition Classes
- any2stringadd
- def ->[B](y: B): (Left[A, B], B)
- Implicit
- This member is added by an implicit conversion from Left[A, B] toArrowAssoc[Left[A, B]] performed by method ArrowAssoc in scala.Predef.
- Definition Classes
- ArrowAssoc
- Annotations
- @inline()
- final def ==(arg0: Any): Boolean
The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.The expression
x == that
is equivalent toif (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
- 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 aClassCastException
at runtime, while the expressionList(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 typeT0
.
- 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.
- final def contains[B1 >: B](elem: B1): Boolean
Returns
true
if this is aRight
and its value is equal toelem
(as determined by==
), returnsfalse
otherwise.Returns
true
if this is aRight
and its value is equal toelem
(as determined by==
), returnsfalse
otherwise.// Returns true because value of Right is "something" which equals "something". Right("something") contains "something" // Returns false because value of Right is "something" which does not equal "anything". Right("something") contains "anything" // Returns false because it's not a Right value. Left("something") contains "something"
- elem
the element to test.
- returns
true
if this is aRight
value equal toelem
.
- Definition Classes
- Either
- def ensuring(cond: (Left[A, B]) => Boolean, msg: => Any): Left[A, B]
- Implicit
- This member is added by an implicit conversion from Left[A, B] toEnsuring[Left[A, B]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
- def ensuring(cond: (Left[A, B]) => Boolean): Left[A, B]
- Implicit
- This member is added by an implicit conversion from Left[A, B] toEnsuring[Left[A, B]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
- def ensuring(cond: Boolean, msg: => Any): Left[A, B]
- Implicit
- This member is added by an implicit conversion from Left[A, B] toEnsuring[Left[A, B]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
- def ensuring(cond: Boolean): Left[A, B]
- Implicit
- This member is added by an implicit conversion from Left[A, B] toEnsuring[Left[A, B]] performed by method Ensuring in scala.Predef.
- Definition Classes
- Ensuring
- 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 ofAnyRef
, and has three additional properties:- It is consistent: for any non-null instances
x
andy
of typeAnyRef
, multiple invocations ofx.eq(y)
consistently returnstrue
or consistently returnsfalse
. - For any non-null instance
x
of typeAnyRef
,x.eq(null)
andnull.eq(x)
returnsfalse
. null.eq(null)
returnstrue
.
When overriding the
equals
orhashCode
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
- It is consistent: for any non-null instances
- def exists(p: (B) => Boolean): Boolean
Returns
false
ifLeft
or returns the result of the application of the given predicate to theRight
value.Returns
false
ifLeft
or returns the result of the application of the given predicate to theRight
value.Right(12).exists(_ > 10) // true Right(7).exists(_ > 10) // false Left(12).exists(_ => true) // false
- Definition Classes
- Either
- def filterOrElse[A1 >: A](p: (B) => Boolean, zero: => A1): Either[A1, B]
Returns
Right
with the existing value ofRight
if this is aRight
and the given predicatep
holds for the right value, orLeft(zero)
if this is aRight
and the given predicatep
does not hold for the right value, orLeft
with the existing value ofLeft
if this is aLeft
.Returns
Right
with the existing value ofRight
if this is aRight
and the given predicatep
holds for the right value, orLeft(zero)
if this is aRight
and the given predicatep
does not hold for the right value, orLeft
with the existing value ofLeft
if this is aLeft
.Right(12).filterOrElse(_ > 10, -1) // Right(12) Right(7).filterOrElse(_ > 10, -1) // Left(-1) Left(7).filterOrElse(_ => false, -1) // Left(7)
- Definition Classes
- Either
- 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 betweenfinalize
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
- def flatMap[A1 >: A, B1](f: (B) => Either[A1, B1]): Either[A1, B1]
Binds the given function across
Right
. - def flatten[A1 >: A, B1](implicit ev: <:<[B, Either[A1, B1]]): Either[A1, B1]
Returns the right value if this is right or this value if this is left
Returns the right value if this is right or this value if this is left
- Definition Classes
- Either
val l: Either[String, Either[String, Int]] = Left("pancake") val rl: Either[String, Either[String, Int]] = Right(Left("flounder")) val rr: Either[String, Either[String, Int]] = Right(Right(7)) l.flatten //Either[String, Int]: Left("pancake") rl.flatten //Either[String, Int]: Left("flounder") rr.flatten //Either[String, Int]: Right(7)
Equivalent to
flatMap(id => id)
Example: - def fold[C](fa: (A) => C, fb: (B) => C): C
Applies
fa
if this is aLeft
orfb
if this is aRight
.Applies
fa
if this is aLeft
orfb
if this is aRight
.- fa
the function to apply if this is a
Left
- fb
the function to apply if this is a
Right
- returns
the results of applying the function
- Definition Classes
- Either
val result = util.Try("42".toInt).toEither result.fold( e => s"Operation failed with $e", v => s"Operation produced value: $v" )
Example: - def forall(f: (B) => Boolean): Boolean
Returns
true
ifLeft
or returns the result of the application of the given predicate to theRight
value.Returns
true
ifLeft
or returns the result of the application of the given predicate to theRight
value.Right(12).forall(_ > 10) // true Right(7).forall(_ > 10) // false Left(12).forall(_ => false) // true
- Definition Classes
- Either
- def foreach[U](f: (B) => U): Unit
Executes the given side-effecting function if this is a
Right
.Executes the given side-effecting function if this is a
Right
.Right(12).foreach(println) // prints "12" Left(12).foreach(println) // doesn't print
- f
The side-effecting function to execute.
- Definition Classes
- Either
- final def getClass(): Class[_ <: AnyRef]
Returns the runtime class representation of the object.
- def getOrElse[B1 >: B](or: => B1): B1
Returns the value from this
Right
or the given argument if this is aLeft
.Returns the value from this
Right
or the given argument if this is aLeft
.Right(12).getOrElse(17) // 12 Left(12).getOrElse(17) // 17
- Definition Classes
- Either
- final def isInstanceOf[T0]: Boolean
Test whether the dynamic type of the receiver object has the same erasure as
T0
.Test whether the dynamic type of the receiver object has the same erasure as
T0
.Depending on what
T0
is, the test is done in one of the below ways:T0
is a non-parameterized class type, e.g.BigDecimal
: this method returnstrue
if the value of the receiver object is aBigDecimal
or a subtype ofBigDecimal
.T0
is a parameterized class type, e.g.List[Int]
: this method returnstrue
if the value of the receiver object is someList[X]
for anyX
. For example,List(1, 2, 3).isInstanceOf[List[String]]
will return true.T0
is some singleton typex.type
or literalx
: this method returnsthis.eq(x)
. For example,x.isInstanceOf[1]
is equivalent tox.eq(1)
T0
is an intersectionX with Y
orX & Y: this method is equivalent to
x.isInstanceOf[X] && x.isInstanceOf[Y]T0
is a unionX | Y
: this method is equivalent tox.isInstanceOf[X] || x.isInstanceOf[Y]
T0
is a type parameter or an abstract type member: this method is equivalent toisInstanceOf[U]
whereU
isT0
's upper bound,Any
ifT0
is unbounded. For example,x.isInstanceOf[A]
whereA
is an unbounded type parameter will return true for any value ofx
.
This is exactly equivalent to the type pattern
_: T0
- returns
true
if the receiver object is an instance of erasure of typeT0
;false
otherwise.
- Definition Classes
- Any
- Note
due to the unexpectedness of
List(1, 2, 3).isInstanceOf[List[String]]
returning true andx.isInstanceOf[A]
whereA
is a type parameter or abstract member returning true, these forms issue a warning.
- def isLeft: Boolean
Returns
true
if this is aLeft
,false
otherwise. - def isRight: Boolean
Returns
true
if this is aRight
,false
otherwise. - def joinLeft[A1 >: A, B1 >: B, C](implicit ev: <:<[A1, Either[C, B1]]): Either[C, B1]
Joins an
Either
throughLeft
.Joins an
Either
throughLeft
.This method requires that the left side of this
Either
is itself anEither
type. That is, this must be some type like:Either[Either[C, B], B]
(which respects the type parameter bounds, shown below.)
If this instance is a
Left[Either[C, B]]
then the containedEither[C, B]
will be returned, otherwise this value will be returned unmodified.Left[Either[Int, String], String](Right("flower")).joinLeft // Result: Right("flower") Left[Either[Int, String], String](Left(12)).joinLeft // Result: Left(12) Right[Either[Int, String], String]("daisy").joinLeft // Result: Right("daisy")
This method, and
joinRight
, are analogous toOption#flatten
.- Definition Classes
- Either
- def joinRight[A1 >: A, B1 >: B, C](implicit ev: <:<[B1, Either[A1, C]]): Either[A1, C]
Joins an
Either
throughRight
.Joins an
Either
throughRight
.This method requires that the right side of this
Either
is itself anEither
type. That is, this must be some type like:Either[A, Either[A, C]]
(which respects the type parameter bounds, shown below.)
If this instance is a
Right[Either[A, C]]
then the containedEither[A, C]
will be returned, otherwise this value will be returned unmodified.- Definition Classes
- Either
Right[String, Either[String, Int]](Right(12)).joinRight // Result: Right(12) Right[String, Either[String, Int]](Left("flower")).joinRight // Result: Left("flower") Left[String, Either[String, Int]]("flower").joinRight // Result: Left("flower")
This method, and
joinLeft
, are analogous toOption#flatten
Example: - def left: LeftProjection[A, B]
Projects this
Either
as aLeft
.Projects this
Either
as aLeft
.This allows for-comprehensions over the left side of
Either
instances, reversingEither
's usual right-bias.For example
for (s <- Left("flower").left) yield s.length // Left(6)
Continuing the analogy with scala.Option, a
LeftProjection
declares thatLeft
should be analogous toSome
in some code.// using Option def interactWithDB(x: Query): Option[Result] = try Some(getResultFromDatabase(x)) catch { case _: SQLException => None } // this will only be executed if interactWithDB returns a Some val report = for (result <- interactWithDB(someQuery)) yield generateReport(result) report match { case Some(r) => send(r) case None => log("report not generated, not sure why...") } // using Either def interactWithDB(x: Query): Either[Exception, Result] = try Right(getResultFromDatabase(x)) catch { case e: SQLException => Left(e) } // run a report only if interactWithDB returns a Right val report = for (result <- interactWithDB(someQuery)) yield generateReport(result) report match { case Right(r) => send(r) case Left(e) => log(s"report not generated, reason was $e") } // only report errors for (e <- interactWithDB(someQuery).left) log(s"query failed, reason was $e")
- Definition Classes
- Either
- def map[B1](f: (B) => B1): Either[A, B1]
The given function is applied if this is a
Right
.The given function is applied if this is a
Right
.Right(12).map(x => "flower") // Result: Right("flower") Left(12).map(x => "flower") // Result: Left(12)
- Definition Classes
- Either
- def merge: B
- Implicit
- This member is added by an implicit conversion from Left[A, B] toMergeableEither[B] performed by method MergeableEither in scala.util.Either.This conversion will take place only if B is a superclass of A (B >: A).
- Definition Classes
- MergeableEither
- 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 orElse[A1 >: A, B1 >: B](or: => Either[A1, B1]): Either[A1, B1]
Returns this
Right
or the given argument if this is aLeft
.Returns this
Right
or the given argument if this is aLeft
.Right(1) orElse Left(2) // Right(1) Left(1) orElse Left(2) // Left(2) Left(1) orElse Left(2) orElse Right(3) // Right(3)
- Definition Classes
- Either
- def productElementNames: Iterator[String]
An iterator over the names of all the elements of this product.
An iterator over the names of all the elements of this product.
- Definition Classes
- Product
- def swap: Either[B, A]
If this is a
Left
, then return the left value inRight
or vice versa.If this is a
Left
, then return the left value inRight
or vice versa.- Definition Classes
- Either
val left: Either[String, Int] = Left("left") val right: Either[Int, String] = left.swap // Result: Right("left")
, val right = Right(2) val left = Left(3) for { r1 <- right r2 <- left.swap } yield r1 * r2 // Right(6)
Examples: - final def synchronized[T0](arg0: => T0): T0
Executes the code in
body
with an exclusive lock onthis
.Executes the code in
body
with an exclusive lock onthis
.- returns
the result of
body
- Definition Classes
- AnyRef
- def toOption: Option[B]
Returns a
Some
containing theRight
value if it exists or aNone
if this is aLeft
.Returns a
Some
containing theRight
value if it exists or aNone
if this is aLeft
.Right(12).toOption // Some(12) Left(12).toOption // None
- Definition Classes
- Either
- def toSeq: collection.immutable.Seq[B]
Returns a
Seq
containing theRight
value if it exists or an emptySeq
if this is aLeft
.Returns a
Seq
containing theRight
value if it exists or an emptySeq
if this is aLeft
.Right(12).toSeq // Seq(12) Left(12).toSeq // Seq()
- Definition Classes
- Either
- def toTry(implicit ev: <:<[A, Throwable]): Try[B]
- Definition Classes
- Either
- val value: A
- final def wait(): Unit
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-
- 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-.
- def withRight[B1 >: B]: Either[A, B1]
Upcasts this
Left[A, B]
toEither[A, B1]
Upcasts this
Left[A, B]
toEither[A, B1]
Left(1) // Either[Int, Nothing] Left(1).withRight[String] // Either[Int, String]
Deprecated Value Members
- def formatted(fmtstr: String): String
Returns string formatted according to given
format
string.Returns string formatted according to given
format
string. Format strings are as forString.format
(@see java.lang.String.format).- Implicit
- This member is added by an implicit conversion from Left[A, B] toStringFormat[Left[A, B]] performed by method StringFormat in scala.Predef.
- Definition Classes
- StringFormat
- Annotations
- @deprecated @inline()
- Deprecated
(Since version 2.12.16) Use
formatString.format(value)
instead ofvalue.formatted(formatString)
, or use thef""
string interpolator. In Java 15 and later,formatted
resolves to the new method in String which has reversed parameters.
- def right: RightProjection[A, B]
Projects this
Either
as aRight
.Projects this
Either
as aRight
.Because
Either
is right-biased, this method is not normally needed.- Definition Classes
- Either
- Annotations
- @deprecated
- Deprecated
(Since version 2.13.0) Either is now right-biased, use methods directly on Either
- def →[B](y: B): (Left[A, B], B)
- Implicit
- This member is added by an implicit conversion from Left[A, B] toArrowAssoc[Left[A, B]] performed by method ArrowAssoc in scala.Predef.
- Definition Classes
- ArrowAssoc
- Annotations
- @deprecated
- Deprecated
(Since version 2.13.0) Use
->
instead. If you still wish to display it as one character, consider using a font with programming ligatures such as Fira Code.
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int
,Float
,Array
orOption
which are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collection
and its sub-packages contain Scala's collections frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.sys
- Interaction with other processes and the operating systemscala.util.matching
- Regular expressionsOther packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
scala.reflect
- Scala's reflection API (scala-reflect.jar)scala.xml
- XML parsing, manipulation, and serialization (scala-xml.jar)scala.collection.parallel
- Parallel collections (scala-parallel-collections.jar)scala.util.parsing
- Parser combinators (scala-parser-combinators.jar)scala.swing
- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)Automatic imports
Identifiers in the scala package and the
scala.Predef
object are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
List
is an alias forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.