Class

scala.util.Either

LeftProjection

Related Doc: package Either

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final case class LeftProjection[+A, +B](e: Either[A, B]) extends Product with Serializable

Projects an Either into a Left.

This allows for-comprehensions over Either instances - 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 ex => None
  }

// this will only be executed if interactWithDB returns a Some
val report =
  for (r <- interactWithDB(someQuery)) yield generateReport(r)
if (report.isDefined)
  send(report)
else
  log("report not generated, not sure why...")
// using Either
def interactWithDB(x: Query): Either[Exception, Result] =
  try {
    Right(getResultFromDatabase(x))
  } catch {
    case ex => Left(ex)
  }

// this will only be executed if interactWithDB returns a Right
val report =
  for (r <- interactWithDB(someQuery).right) yield generateReport(r)
if (report.isRight)
  send(report)
else
  log("report not generated, reason was " + report.left.get)
Version

1.0, 11/10/2008

Linear Supertypes
Serializable, java.io.Serializable, Product, Equals, AnyRef, Any
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Inherited
  1. LeftProjection
  2. Serializable
  3. Serializable
  4. Product
  5. Equals
  6. AnyRef
  7. Any
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Visibility
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Instance Constructors

  1. new LeftProjection(e: Either[A, B])

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Value Members

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

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    Definition Classes
    AnyRef → Any

  2. final def ##(): Int

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    Definition Classes
    AnyRef → Any

  3. final def ==(arg0: Any): Boolean

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    Definition Classes
    AnyRef → Any

  4. final def asInstanceOf[T0]: T0

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    Definition Classes
    Any

  5. def clone(): AnyRef

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

  6. val e: Either[A, B]

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  7. final def eq(arg0: AnyRef): Boolean

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    Definition Classes
    AnyRef

  8. def exists(p: (A) ⇒ Boolean): Boolean

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    Returns false if Right or returns the result of the application of the given function to the Left value.

    Returns false if Right or returns the result of the application of the given function to the Left value.

    Left(12).left.exists(_ > 10)  // true
Left(7).left.exists(_ > 10)   // false
Right(12).left.exists(_ > 10) // false

  9. def filter[Y](p: (A) ⇒ Boolean): Option[Either[A, Y]]

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    Returns None if this is a Right or if the given predicate p does not hold for the left value, otherwise, returns a Left.

    Returns None if this is a Right or if the given predicate p does not hold for the left value, otherwise, returns a Left.

    Left(12).left.filter(_ > 10)  // Some(Left(12))
Left(7).left.filter(_ > 10)   // None
Right(12).left.filter(_ > 10) // None

  10. def finalize(): Unit

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

  11. def flatMap[BB >: B, X](f: (A) ⇒ Either[X, BB]): Either[X, BB]

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    Binds the given function across Left.

    Binds the given function across Left.

    Left(12).left.flatMap(x => Left("scala")) // Left("scala")
Right(12).left.flatMap(x => Left("scala") // Right(12)
    f

    The function to bind across Left.

  12. def forall(p: (A) ⇒ Boolean): Boolean

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

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

    Left(12).left.forall(_ > 10)  // true
Left(7).left.forall(_ > 10)   // false
Right(12).left.forall(_ > 10) // true

  13. def foreach[U](f: (A) ⇒ U): Any

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    Executes the given side-effecting function if this is a Left.

    Executes the given side-effecting function if this is a Left.

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

    The side-effecting function to execute.

  14. def get: A

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    Returns the value from this Left or throws java.util.NoSuchElementException if this is a Right.

    Returns the value from this Left or throws java.util.NoSuchElementException if this is a Right.

    Left(12).left.get // 12
Right(12).left.get // NoSuchElementException
    Exceptions thrown

    java.util.NoSuchElementException if the projection is scala.util.Right

  15. final def getClass(): Class[_]

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    Definition Classes
    AnyRef → Any

  16. def getOrElse[AA >: A](or: ⇒ AA): AA

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

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

    Left(12).left.getOrElse(17)  // 12
Right(12).left.getOrElse(17) // 17

  17. final def isInstanceOf[T0]: Boolean

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    Definition Classes
    Any

  18. def map[X](f: (A) ⇒ X): Product with Serializable with Either[X, B]

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    Maps the function argument through Left.

    Maps the function argument through Left.

    Left(12).left.map(_ + 2) // Left(14)
Right[Int, Int](12).left.map(_ + 2) // Right(12)

  19. final def ne(arg0: AnyRef): Boolean

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    Definition Classes
    AnyRef

  20. final def notify(): Unit

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    Definition Classes
    AnyRef

  21. final def notifyAll(): Unit

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    Definition Classes
    AnyRef

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

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    Definition Classes
    AnyRef

  23. def toOption: Option[A]

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

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

    Left(12).left.toOption // Some(12)
Right(12).left.toOption // None

  24. def toSeq: collection.Seq[A]

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

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

    Left(12).left.toSeq // Seq(12)
Right(12).left.toSeq // Seq()

  25. final def wait(): Unit

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    Definition Classes
    AnyRef
    Annotations
    @throws( ... )

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

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    Definition Classes
    AnyRef
    Annotations
    @throws( ... )

  27. final def wait(arg0: Long): Unit

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    Definition Classes
    AnyRef
    Annotations
    @throws( ... )

Inherited from Serializable

Inherited from java.io.Serializable

Inherited from Product

Inherited from Equals

Inherited from AnyRef

Inherited from Any

Ungrouped