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 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

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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 any2stringfmt
  3. by any2ArrowAssoc
  4. by any2Ensuring
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  1. Public
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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

    Test two objects for inequality.

    Test two objects for inequality.

    returns

    true if !(this == that), false otherwise.

    Definition Classes
    Any
  3. 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
  4. def +(other: String): String

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to StringAdd performed by method any2stringadd 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 any2ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  6. final def ==(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef
  7. final def ==(arg0: Any): Boolean

    Test two objects for equality.

    Test two objects for equality. 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
    Any
  8. 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.

  9. 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[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  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 any2Ensuring 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 any2Ensuring 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 any2Ensuring 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 any2Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  15. final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (arg0) is a reference to the receiver object (this).

    Tests whether the argument (arg0) 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
  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

    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[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  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 performed by method any2stringfmt 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.Right

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

    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

  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

    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
  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

    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
  29. 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
    Note

    not specified by SLS as a member of AnyRef

  30. 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
    Note

    not specified by SLS as a member of 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: 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 any2ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc

Shadowed Implict Value Members

  1. val self: Any

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to StringAdd performed by method any2stringadd in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (leftProjection: StringAdd).self
    Definition Classes
    StringAdd
  2. val self: Any

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to StringFormat performed by method any2stringfmt in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (leftProjection: StringFormat).self
    Definition Classes
    StringFormat

Deprecated Value Members

  1. def x: LeftProjection[A, B]

    Implicit information
    This member is added by an implicit conversion from LeftProjection[A, B] to ArrowAssoc[LeftProjection[A, B]] performed by method any2ArrowAssoc in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (leftProjection: ArrowAssoc[LeftProjection[A, B]]).x
    Definition Classes
    ArrowAssoc
    Annotations
    @deprecated
    Deprecated

    (Since version 2.10.0) Use leftOfArrow instead

  2. def x: 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 any2Ensuring in scala.Predef.
    Shadowing
    This implicitly inherited member is ambiguous. One or more implicitly inherited members have similar signatures, so calling this member may produce an ambiguous implicit conversion compiler error.
    To access this member you can use a type ascription:
    (leftProjection: Ensuring[LeftProjection[A, B]]).x
    Definition Classes
    Ensuring
    Annotations
    @deprecated
    Deprecated

    (Since version 2.10.0) Use resultOfEnsuring instead

Inherited from Serializable

Inherited from Serializable

Inherited from Product

Inherited from Equals

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd from LeftProjection[A, B] to StringAdd

Inherited by implicit conversion any2stringfmt from LeftProjection[A, B] to StringFormat

Inherited by implicit conversion any2ArrowAssoc from LeftProjection[A, B] to ArrowAssoc[LeftProjection[A, B]]

Inherited by implicit conversion any2Ensuring from LeftProjection[A, B] to Ensuring[LeftProjection[A, B]]