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)
- Annotations
- @deprecated
- Deprecated
(Since version 2.12.0) use swap instead
- Source
- Either.scala
- Version
1.0, 11/10/2008
- Alphabetic
- By Inheritance
- LeftProjection
- Serializable
- Serializable
- Product
- Equals
- AnyRef
- Any
- by any2stringadd
- by StringFormat
- by Ensuring
- by ArrowAssoc
- Hide All
- Show All
- Public
- All
Value Members
-
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
-
final
def
##(): Int
Equivalent to
x.hashCode
except for boxed numeric types andnull
.Equivalent to
x.hashCode
except for boxed numeric types andnull
. 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. Fornull
returns a hashcode wherenull.hashCode
throws aNullPointerException
.- returns
a hash value consistent with ==
- Definition Classes
- AnyRef → Any
-
def
+(other: String): String
- Implicit
- 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
-
def
->[B](y: B): (LeftProjection[A, B], B)
- Implicit
- 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()
-
final
def
==(arg0: Any): Boolean
The expression
x == that
is equivalent toif (x eq null) that eq null else x.equals(that)
.The expression
x == that
is equivalent toif (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
-
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 aClassCastException
at runtime, while the expressionList(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 typeT0
.
-
def
clone(): AnyRef
Create a copy of the receiver object.
- val e: Either[A, B]
-
def
ensuring(cond: (LeftProjection[A, B]) ⇒ Boolean, msg: ⇒ Any): LeftProjection[A, B]
- Implicit
- 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
-
def
ensuring(cond: (LeftProjection[A, B]) ⇒ Boolean): LeftProjection[A, B]
- Implicit
- 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
-
def
ensuring(cond: Boolean, msg: ⇒ Any): LeftProjection[A, B]
- Implicit
- 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
-
def
ensuring(cond: Boolean): LeftProjection[A, B]
- Implicit
- 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
-
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 ofAnyRef
, and has three additional properties:- It is consistent: for any non-null instances
x
andy
of typeAnyRef
, multiple invocations ofx.eq(y)
consistently returnstrue
or consistently returnsfalse
. - For any non-null instance
x
of typeAnyRef
,x.eq(null)
andnull.eq(x)
returnsfalse
. null.eq(null)
returnstrue
.
When overriding the
equals
orhashCode
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
- It is consistent: for any non-null instances
-
def
exists(p: (A) ⇒ Boolean): Boolean
Returns
false
ifRight
or returns the result of the application of the given function to theLeft
value.Returns
false
ifRight
or returns the result of the application of the given function to theLeft
value.Left(12).left.exists(_ > 10) // true Left(7).left.exists(_ > 10) // false Right(12).left.exists(_ > 10) // false
-
def
filter[Y](p: (A) ⇒ Boolean): Option[Either[A, Y]]
Returns
None
if this is aRight
or if the given predicatep
does not hold for the left value, otherwise, returns aLeft
.Returns
None
if this is aRight
or if the given predicatep
does not hold for the left value, otherwise, returns aLeft
.Left(12).left.filter(_ > 10) // Some(Left(12)) Left(7).left.filter(_ > 10) // None Right(12).left.filter(_ > 10) // None
-
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 betweenfinalize
and non-local returns and exceptions, are all platform dependent. -
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
.
-
def
forall(p: (A) ⇒ Boolean): Boolean
Returns
true
ifRight
or returns the result of the application of the given function to theLeft
value.Returns
true
ifRight
or returns the result of the application of the given function to theLeft
value.Left(12).left.forall(_ > 10) // true Left(7).left.forall(_ > 10) // false Right(12).left.forall(_ > 10) // true
-
def
foreach[U](f: (A) ⇒ U): Unit
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.
-
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 forString.format
(@see java.lang.String.format).- Implicit
- 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()
-
def
get: A
Returns the value from this
Left
or throwsjava.util.NoSuchElementException
if this is aRight
.Returns the value from this
Left
or throwsjava.util.NoSuchElementException
if this is aRight
.Left(12).left.get // 12 Right(12).left.get // NoSuchElementException
- Exceptions thrown
java.util.NoSuchElementException
if the projection is scala.util.Right
-
final
def
getClass(): Class[_]
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
-
def
getOrElse[AA >: A](or: ⇒ AA): AA
Returns the value from this
Left
or the given argument if this is aRight
.Returns the value from this
Left
or the given argument if this is aRight
.Left(12).left.getOrElse(17) // 12 Right(12).left.getOrElse(17) // 17
-
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 returnfalse
, while the expressionList(1).isInstanceOf[List[String]]
will returntrue
. 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 typeT0
;false
otherwise.
- Definition Classes
- Any
-
def
map[X](f: (A) ⇒ X): 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)
-
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
-
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
-
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
-
final
def
synchronized[T0](arg0: ⇒ T0): T0
- Definition Classes
- AnyRef
-
def
toOption: Option[A]
Returns a
Some
containing theLeft
value if it exists or aNone
if this is aRight
.Returns a
Some
containing theLeft
value if it exists or aNone
if this is aRight
.Left(12).left.toOption // Some(12) Right(12).left.toOption // None
-
def
toSeq: Seq[A]
Returns a
Seq
containing theLeft
value if it exists or an emptySeq
if this is aRight
.Returns a
Seq
containing theLeft
value if it exists or an emptySeq
if this is aRight
.Left(12).left.toSeq // Seq(12) Right(12).left.toSeq // Seq()
-
final
def
wait(): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
-
final
def
wait(arg0: Long, arg1: Int): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
-
final
def
wait(arg0: Long): Unit
- Definition Classes
- AnyRef
- Annotations
- @throws( ... )
-
def
→[B](y: B): (LeftProjection[A, B], B)
- Implicit
- 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
This is the documentation for the Scala standard library.
Package structure
The scala package contains core types like
Int
,Float
,Array
orOption
which are accessible in all Scala compilation units without explicit qualification or imports.Notable packages include:
scala.collection
and its sub-packages contain Scala's collections frameworkscala.collection.immutable
- Immutable, sequential data-structures such asVector
,List
,Range
,HashMap
orHashSet
scala.collection.mutable
- Mutable, sequential data-structures such asArrayBuffer
,StringBuilder
,HashMap
orHashSet
scala.collection.concurrent
- Mutable, concurrent data-structures such asTrieMap
scala.collection.parallel.immutable
- Immutable, parallel data-structures such asParVector
,ParRange
,ParHashMap
orParHashSet
scala.collection.parallel.mutable
- Mutable, parallel data-structures such asParArray
,ParHashMap
,ParTrieMap
orParHashSet
scala.concurrent
- Primitives for concurrent programming such asFutures
andPromises
scala.io
- Input and output operationsscala.math
- Basic math functions and additional numeric types likeBigInt
andBigDecimal
scala.sys
- Interaction with other processes and the operating systemscala.util.matching
- Regular expressionsOther packages exist. See the complete list on the right.
Additional parts of the standard library are shipped as separate libraries. These include:
scala.reflect
- Scala's reflection API (scala-reflect.jar)scala.xml
- XML parsing, manipulation, and serialization (scala-xml.jar)scala.swing
- A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)scala.util.parsing
- Parser combinators, including an example implementation of a JSON parser (scala-parser-combinators.jar)Automatic imports
Identifiers in the scala package and the
scala.Predef
object are always in scope by default.Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example,
List
is an alias forscala.collection.immutable.List
.Other aliases refer to classes provided by the underlying platform. For example, on the JVM,
String
is an alias forjava.lang.String
.