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Class scala.util.Left

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
Linear Supertypes
Either[A, B], java.io.Serializable, Product, Equals, AnyRef, Any

Instance Constructors

new Left(value: A)

Value Members

final def !=(arg0: Any): Boolean

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. 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

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 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

final def asInstanceOf[T0]: 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.

def clone(): AnyRef

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[java.lang]
Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.CloneNotSupportedException]) @native()
Note

not specified by SLS as a member of AnyRef

final def contains[B1 >: B](elem: B1): Boolean

Returns true if this is a Right and its value is equal to elem (as determined by ==), returns false 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 a Right value equal to elem.

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).

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 exists(p: (B) => Boolean): Boolean

Returns false if Left or returns the result of the application of the given predicate to the Right 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 of Right if this is a Right and the given predicate p holds for the right value, or Left(zero) if this is a Right and the given predicate p does not hold for the right value, or Left with the existing value of Left if this is a Left.

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.

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[java.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.

f

The function to bind across Right.

Definition Classes
Either

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

Definition Classes
Either
Example:
    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)

def fold[C](fa: (A) => C, fb: (B) => C): C

Applies fa if this is a Left or fb if this is a Right.

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
Example:
    val result = util.Try("42".toInt).toEither
    result.fold(
      e => s"Operation failed with $e",
      v => s"Operation produced value: $v"
    )

def forall(f: (B) => Boolean): Boolean

Returns true if Left or returns the result of the application of the given predicate to the Right 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.

Right(12).foreach(println) // prints "12"
Left(12).foreach(println)  // doesn't print
f

The side-effecting function to execute.

Definition Classes
Either

def formatted(fmtstr: String): String

Returns string formatted according to given format string. Format strings are as for String.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
@inline()

final def getClass(): Class[_ <: AnyRef]

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 getOrElse[B1 >: B](or: => B1): B1

Returns the value from this Right or the given argument if this is a Left.

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 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 isLeft: Boolean

Returns true if this is a Left, false otherwise.

Left("tulip").isLeft // true
Right("venus fly-trap").isLeft // false
Definition Classes
LeftEither

def isRight: Boolean

Returns true if this is a Right, false otherwise.

Left("tulip").isRight // false
Right("venus fly-trap").isRight // true
Definition Classes
LeftEither

def joinLeft[A1 >: A, B1 >: B, C](implicit ev: <:<[A1, Either[C, B1]]): Either[C, B1]

Joins an Either through Left.

This method requires that the left side of this Either is itself an Either 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 contained Either[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 to Option#flatten.

Definition Classes
Either

def joinRight[A1 >: A, B1 >: B, C](implicit ev: <:<[B1, Either[A1, C]]): Either[A1, C]

Joins an Either through Right.

This method requires that the right side of this Either is itself an Either 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 contained Either[A, C] will be returned, otherwise this value will be returned unmodified.

Definition Classes
Either
Example:
    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 to Option#flatten

def left: LeftProjection[A, B]

Projects this Either as a Left.

This allows for-comprehensions over the left side of Either instances, reversing Either'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 that Left should be analogous to Some 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.

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).

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.

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.

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 a Left.

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.

Definition Classes
Product

def swap: Either[B, A]

If this is a Left, then return the left value in Right or vice versa.

Definition Classes
Either
Examples:
    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)

final def synchronized[T0](arg0: => T0): T0

Definition Classes
AnyRef

def toOption: Option[B]

Returns a Some containing the Right value if it exists or a None if this is a Left.

Right(12).toOption // Some(12)
Left(12).toOption  // None
Definition Classes
Either

def toSeq: collection.immutable.Seq[B]

Returns a Seq containing the Right value if it exists or an empty Seq if this is a Left.

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

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

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

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException])

final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws(classOf[java.lang.InterruptedException]) @native()

def withRight[B1 >: B]: Either[A, B1]

Upcasts this Left[A, B] to Either[A, B1]

Left(1)                   // Either[Int, Nothing]
Left(1).withRight[String] // Either[Int, String]

© 2002-2019 EPFL, with contributions from Lightbend.
Licensed under the Apache License, Version 2.0.
https://www.scala-lang.org/api/2.13.0/scala/util/Left.html