Packages

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
Type Hierarchy
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Inherited
  1. Left
  2. Either
  3. Serializable
  4. Product
  5. Equals
  6. AnyRef
  7. Any
Implicitly
  1. by MergeableEither
  2. by any2stringadd
  3. by StringFormat
  4. by Ensuring
  5. by ArrowAssoc
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Visibility
  1. Public
  2. All

Instance Constructors

  1. new Left(value: A)

Value Members

  1. 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
  2. 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
  3. 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
  4. 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()
  5. 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
  6. 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.

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

    not specified by SLS as a member of AnyRef

  8. 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 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. 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.

    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
  15. 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.

    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
  16. 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[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.Throwable])
    Note

    not specified by SLS as a member of AnyRef

  17. def flatMap[A1 >: A, B1](f: (B) => Either[A1, B1]): Either[A1, B1]

    Binds the given function across Right.

    Binds the given function across Right.

    f

    The function to bind across Right.

    Definition Classes
    Either
  18. 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
    Example:
    1. 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)

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

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

    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:
    1. val result = util.Try("42".toInt).toEither
      result.fold(
        e => s"Operation failed with $e",
        v => s"Operation produced value: $v"
      )
  20. 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.

    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
  21. 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
  22. 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 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()
  23. final def getClass(): 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()
  24. def getOrElse[B1 >: B](or: => B1): B1

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

    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
  25. 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
  26. def isLeft: Boolean

    Returns true if this is a Left, false otherwise.

    Returns true if this is a Left, false otherwise.

    Left("tulip").isLeft // true
    Right("venus fly-trap").isLeft // false
    Definition Classes
    LeftEither
  27. def isRight: Boolean

    Returns true if this is a Right, false otherwise.

    Returns true if this is a Right, false otherwise.

    Left("tulip").isRight // false
    Right("venus fly-trap").isRight // true
    Definition Classes
    LeftEither
  28. def joinLeft[A1 >: A, B1 >: B, C](implicit ev: <:<[A1, Either[C, B1]]): Either[C, B1]

    Joins an Either through Left.

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

    Joins an Either through Right.

    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:
    1. 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

  30. def left: LeftProjection[A, B]

    Projects this Either as a Left.

    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
  31. 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
  32. 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
  33. 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
  34. 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

  35. 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

  36. 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.

    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
  37. 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
  38. def swap: Either[B, A]

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

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

    Definition Classes
    Either
    Examples:
    1. val left: Either[String, Int]  = Left("left")
      val right: Either[Int, String] = left.swap // Result: Right("left")
    2. ,
    3. val right = Right(2)
      val left  = Left(3)
      for {
        r1 <- right
        r2 <- left.swap
      } yield r1 * r2 // Right(6)
  39. final def synchronized[T0](arg0: => T0): T0
    Definition Classes
    AnyRef
  40. def toOption: Option[B]

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

    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
  41. 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.

    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
  42. def toTry(implicit ev: <:<[A, Throwable]): Try[B]
    Definition Classes
    Either
  43. val value: A
  44. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException])
  45. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException])
  46. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws(classOf[java.lang.InterruptedException]) @native()
  47. def withRight[B1 >: B]: Either[A, B1]

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

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

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

Deprecated Value Members

  1. def right: RightProjection[A, B]

    Projects this Either as a Right.

    Projects this Either as a Right.

    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

  2. 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.

Inherited from Either[A, B]

Inherited from java.io.Serializable

Inherited from Product

Inherited from Equals

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion MergeableEither fromLeft[A, B] to MergeableEither[B]

Inherited by implicit conversion any2stringadd fromLeft[A, B] to any2stringadd[Left[A, B]]

Inherited by implicit conversion StringFormat fromLeft[A, B] to StringFormat[Left[A, B]]

Inherited by implicit conversion Ensuring fromLeft[A, B] to Ensuring[Left[A, B]]

Inherited by implicit conversion ArrowAssoc fromLeft[A, B] to ArrowAssoc[Left[A, B]]

Ungrouped