scala.util.Either

LeftProjection

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
Type Hierarchy Learn more about scaladoc diagrams
Ordering
  1. Alphabetic
  2. By inheritance
Inherited
  1. LeftProjection
  2. Serializable
  3. Serializable
  4. Product
  5. Equals
  6. AnyRef
  7. Any
Implicitly
  1. by StringAdd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
  1. Hide All
  2. Show all
Learn more about member selection
Visibility
  1. Public
  2. All

Instance Constructors

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

Value Members

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

    Definition Classes
    AnyRef

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

    Definition Classes
    Any

  3. final def ##(): Int

    Definition Classes
    AnyRef → Any

  4. def +(other: String): String

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to StringAdd[LeftProjection[A, B]] performed by method StringAdd in scala.Predef.
    Definition Classes
    StringAdd

  5. def ->[B](y: B): (LeftProjection[A, B], B)

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to ArrowAssoc[LeftProjection[A, B]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()

  6. final def ==(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef

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

    Definition Classes
    Any

  8. final def asInstanceOf[T0]: T0

    Definition Classes
    Any

  9. def clone(): AnyRef

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

  10. val e: Either[A, B]

  11. def ensuring(cond: (LeftProjection[A, B]) ⇒ Boolean, msg: ⇒ Any): LeftProjection[A, B]

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to Ensuring[LeftProjection[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring

  12. def ensuring(cond: (LeftProjection[A, B]) ⇒ Boolean): LeftProjection[A, B]

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to Ensuring[LeftProjection[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring

  13. def ensuring(cond: Boolean, msg: ⇒ Any): LeftProjection[A, B]

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to Ensuring[LeftProjection[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring

  14. def ensuring(cond: Boolean): LeftProjection[A, B]

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to Ensuring[LeftProjection[A, B]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring

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

    Definition Classes
    AnyRef

  16. def exists(f: (A) ⇒ Boolean): Boolean

    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

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

    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

  18. def finalize(): Unit

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

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

    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.

  20. def forall(f: (A) ⇒ Boolean): Boolean

    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

  21. def foreach[U](f: (A) ⇒ U): Any

    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.

  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 information
    This member is added by an implicit conversion from LeftProjection[A, B] to StringFormat[LeftProjection[A, B]] performed by method StringFormat in scala.Predef.
    Definition Classes
    StringFormat
    Annotations
    @inline()

  23. def get: A

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

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

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

    if the projection is scala.util.Right

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

    Definition Classes
    AnyRef → Any

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

    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

  26. final def isInstanceOf[T0]: Boolean

    Definition Classes
    Any

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

    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)

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

    Definition Classes
    AnyRef

  29. final def notify(): Unit

    Definition Classes
    AnyRef

  30. final def notifyAll(): Unit

    Definition Classes
    AnyRef

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

    Definition Classes
    AnyRef

  32. def toOption: Option[A]

    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

  33. def toSeq: collection.Seq[A]

    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()

  34. final def wait(): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws( ... )

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

    Definition Classes
    AnyRef
    Annotations
    @throws( ... )

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

    Definition Classes
    AnyRef
    Annotations
    @throws( ... )

  37. def →[B](y: B): (LeftProjection[A, B], B)

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to ArrowAssoc[LeftProjection[A, B]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc

Inherited from Serializable

Inherited from java.io.Serializable

Inherited from Product

Inherited from Equals

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion StringAdd from LeftProjection[A, B] to StringAdd[LeftProjection[A, B]]

Inherited by implicit conversion StringFormat from LeftProjection[A, B] to StringFormat[LeftProjection[A, B]]

Inherited by implicit conversion Ensuring from LeftProjection[A, B] to Ensuring[LeftProjection[A, B]]

Inherited by implicit conversion ArrowAssoc from LeftProjection[A, B] to ArrowAssoc[LeftProjection[A, B]]

Ungrouped