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)
Source
Either.scala
Version

1.0, 11/10/2008

Linear Supertypes
Serializable, java.io.Serializable, Product, Equals, AnyRef, Any
Ordering
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Inherited
  1. LeftProjection
  2. Serializable
  3. Serializable
  4. Product
  5. Equals
  6. AnyRef
  7. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Visibility
  1. Public
  2. All

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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    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

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    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

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    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to any2stringadd[LeftProjection[A, B]] performed by method any2stringadd in scala.Predef.
    Definition Classes
    any2stringadd
  4. def ->[B](y: B): (LeftProjection[A, B], B)

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

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    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

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    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

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    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( ... )
    Note

    not specified by SLS as a member of AnyRef

  8. val e: Either[A, B]

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

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

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

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    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: Boolean): LeftProjection[A, B]

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    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. final def eq(arg0: AnyRef): Boolean

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    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: (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
  15. 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
  16. def finalize(): Unit

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    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[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.

  18. 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
  19. 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.

  20. def formatted(fmtstr: String): String

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    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()
  21. 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

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

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    A representation that corresponds to the dynamic class of the receiver object.

    A representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

    a representation that corresponds to the dynamic class of the receiver object.

    Definition Classes
    AnyRef → Any
    Note

    not specified by SLS as a member of AnyRef

  23. 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
  24. final def isInstanceOf[T0]: Boolean

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    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
  25. def map[X](f: (A) ⇒ X): Serializable with Product 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)
  26. final def ne(arg0: AnyRef): Boolean

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    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
  27. final def notify(): Unit

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    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
    Note

    not specified by SLS as a member of AnyRef

  28. final def notifyAll(): Unit

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    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
    Note

    not specified by SLS as a member of AnyRef

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

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    Definition Classes
    AnyRef
  30. 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
  31. 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()
  32. final def wait(): Unit

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    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  33. final def wait(arg0: Long, arg1: Int): Unit

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    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  34. final def wait(arg0: Long): Unit

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    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  35. def [B](y: B): (LeftProjection[A, B], B)

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    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 any2stringadd from LeftProjection[A, B] to any2stringadd[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