Either (Vavr 0.10.0 API)

Type Parameters:

L - The type of the Left value of an Either.

R - The type of the Right value of an Either.

All Superinterfaces:

Iterable<R>, Serializable, Value<R>

All Known Implementing Classes:

Either.Left, Either.Right
```
public interface Either<L,R>
extends Value<R>, Serializable
```
Either represents a value of two possible types. An Either is either a Either.Left or a Either.Right.
If the given Either is a Right and projected to a Left, the Left operations have no effect on the Right value.
If the given Either is a Left and projected to a Right, the Right operations have no effect on the Left value.
If a Left is projected to a Left or a Right is projected to a Right, the operations have an effect.
Example: A compute() function, which results either in an Integer value (in the case of success) or in an error message of type String (in the case of failure). By convention the success case is Right and the failure is Left.
```
 
 Either<String,Integer> value = compute().right().map(i -> i * 2).toEither();
 
 
```
If the result of compute() is Right(1), the value is Right(2).
If the result of compute() is Left("error"), the value is Left("error").
Author:

Daniel Dietrich

Nested Class Summary

Nested Classes
Modifier and Type	Interface and Description
`static class`	`Either.Left<L,R>` The `Left` version of an `Either`.
`static class`	`Either.LeftProjection<L,R>` Deprecated. Either is right-biased. Use `swap()` instead of projections.
`static class`	`Either.Right<L,R>` The `Right` version of an `Either`.
`static class`	`Either.RightProjection<L,R>` Deprecated. Either is right-biased. Use `swap()` instead of projections.

Field Summary

Fields
Modifier and Type Field and Description

static long serialVersionUID

Fields
Modifier and Type	Field and Description
`static long`	`serialVersionUID`

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Default Methods Deprecated Methods
Modifier and Type	Method and Description
`default <X,Y> Either<X,Y>`	`bimap(Function<? super L,? extends X> leftMapper, Function<? super R,? extends Y> rightMapper)` Maps either the left or the right side of this disjunction.
`boolean`	`equals(Object o)` Clarifies that values have a proper equals() method implemented.
`default Option<Either<L,R>>`	`filter(Predicate<? super R> predicate)` Filters this right-biased `Either` by testing a predicate.
`default Either<L,R>`	`filterOrElse(Predicate<? super R> predicate, Function<? super R,? extends L> zero)` Filters this right-biased `Either` by testing a predicate.
`default <U> Either<L,U>`	`flatMap(Function<? super R,? extends Either<L,? extends U>> mapper)` FlatMaps this right-biased Either.
`default <U> U`	`fold(Function<? super L,? extends U> leftMapper, Function<? super R,? extends U> rightMapper)` Folds either the left or the right side of this disjunction.
`R`	`get()` Gets the right value if this is a `Right` or throws if this is a `Left`.
`L`	`getLeft()` Returns the left value.
`default R`	`getOrElseGet(Function<? super L,? extends R> other)` Gets the Right value or an alternate value, if the projected Either is a Left.
`default <X extends Throwable> R`	`getOrElseThrow(Function<? super L,X> exceptionFunction)` Gets the Right value or throws, if the projected Either is a Left.
`int`	`hashCode()` Clarifies that values have a proper hashCode() method implemented.
`default boolean`	`isAsync()` A right-biased `Either`'s value is computed synchronously.
`default boolean`	`isEmpty()` Checks, this `Value` is empty, i.e.
`default boolean`	`isLazy()` A right-biased `Either`'s value is computed eagerly.
`boolean`	`isLeft()` Returns whether this Either is a Left.
`boolean`	`isRight()` Returns whether this Either is a Right.
`default boolean`	`isSingleValued()` A right-biased `Either` is single-valued.
`default Iterator<R>`	`iterator()` Returns a rich `io.vavr.collection.Iterator`.
`default Either.LeftProjection<L,R>`	`left()` Deprecated. Either is right-biased. Use `swap()` instead of projections.
`static <L,R> Either<L,R>`	`left(L left)` Constructs a `Either.Left`
`default <U> Either<L,U>`	`map(Function<? super R,? extends U> mapper)` Maps the value of this Either if it is a Right, performs no operation if this is a Left.
`default <U> Either<U,R>`	`mapLeft(Function<? super L,? extends U> leftMapper)` Maps the value of this Either if it is a Left, performs no operation if this is a Right.
`static <L,R> Either<L,R>`	`narrow(Either<? extends L,? extends R> either)` Narrows a widened `Either<? extends L, ? extends R>` to `Either<L, R>` by performing a type-safe cast.
`default Either<L,R>`	`orElse(Either<? extends L,? extends R> other)`
`default Either<L,R>`	`orElse(Supplier<? extends Either<? extends L,? extends R>> supplier)`
`default void`	`orElseRun(Consumer<? super L> action)` Runs an action in the case this is a projection on a Left value.
`default Either<L,R>`	`peek(Consumer<? super R> action)` Performs the given `action` on the first element if this is an eager implementation.
`default Either<L,R>`	`peekLeft(Consumer<? super L> action)`
`default Either.RightProjection<L,R>`	`right()` Deprecated. Either is right-biased. Use `swap()` instead of projections.
`static <L,R> Either<L,R>`	`right(R right)` Constructs a `Either.Right`
`static <L,R> Either<Seq<L>,Seq<R>>`	`sequence(Iterable<? extends Either<? extends L,? extends R>> eithers)` Reduces many `Either`s into a single `Either` by transforming an `Iterable<Either<L, R>>` into a `Either<Seq<L>, Seq<R>>`.
`static <L,R> Either<L,Seq<R>>`	`sequenceRight(Iterable<? extends Either<? extends L,? extends R>> eithers)` Reduces many `Either`s into a single `Either` by transforming an `Iterable<Either<L, R>>` into a `Either<L, Seq<R>>`.
`default Either<R,L>`	`swap()` Converts a `Left` to a `Right` vice versa by wrapping the value in a new type.
`String`	`toString()` Clarifies that values have a proper toString() method implemented.
`default Validation<L,R>`	`toValidation()` Returns this as `Validation`.
`static <L,R,T> Either<Seq<L>,Seq<R>>`	`traverse(Iterable<? extends T> values, Function<? super T,? extends Either<? extends L,? extends R>> mapper)` Maps the values of an iterable to a sequence of mapped values into a single `Either` by transforming an `Iterable<? extends T>` into a `Either<Seq<U>>`.
`static <L,R,T> Either<L,Seq<R>>`	`traverseRight(Iterable<? extends T> values, Function<? super T,? extends Either<? extends L,? extends R>> mapper)` Maps the values of an iterable to a sequence of mapped values into a single `Either` by transforming an `Iterable<? extends T>` into a `Either<Seq<U>>`.

Methods inherited from interface io.vavr.Value
collect, collect, contains, corresponds, eq, exists, forAll, forEach, getOrElse, getOrElse, getOrElseThrow, getOrElseTry, getOrNull, narrow, out, out, spliterator, stderr, stdout, stringPrefix, toArray, toCharSeq, toCompletableFuture, toEither, toEither, toInvalid, toInvalid, toJavaArray, toJavaArray, toJavaArray, toJavaCollection, toJavaList, toJavaList, toJavaMap, toJavaMap, toJavaMap, toJavaOptional, toJavaParallelStream, toJavaSet, toJavaSet, toJavaStream, toLeft, toLeft, toLinkedMap, toLinkedMap, toLinkedSet, toList, toMap, toMap, toOption, toPriorityQueue, toPriorityQueue, toQueue, toRight, toRight, toSet, toSortedMap, toSortedMap, toSortedMap, toSortedMap, toSortedSet, toSortedSet, toStream, toTree, toTree, toTry, toTry, toValid, toValid, toValidation, toValidation, toVector

- Field Detail
 - serialVersionUID
```
static final long serialVersionUID
```
 See Also:
 
 Constant Field Values
- Method Detail
 - right
```
static <L,R> Either<L,R> right(R right)
```
 Constructs a Either.Right
 
 Type Parameters:
 
 L - Type of left value.
 
 R - Type of right value.
 
 Parameters:
 
 right - The value.
 
 Returns:
 
 A new Right instance.
 - left
```
static <L,R> Either<L,R> left(L left)
```
 Constructs a Either.Left
 
 Type Parameters:
 
 L - Type of left value.
 
 R - Type of right value.
 
 Parameters:
 
 left - The value.
 
 Returns:
 
 A new Left instance.
 - narrow
```
static <L,R> Either<L,R> narrow(Either<? extends L,? extends R> either)
```
 Narrows a widened Either<? extends L, ? extends R> to Either<L, R> by performing a type-safe cast. This is eligible because immutable/read-only collections are covariant.
 
 Type Parameters:
 
 L - Type of left value.
 
 R - Type of right value.
 
 Parameters:
 
 either - A Either.
 
 Returns:
 
 the given either instance as narrowed type Either<L, R>.
 - getLeft
```
L getLeft()
```
 Returns the left value.
 
 Returns:
 
 The left value.
 
 Throws:
 
 NoSuchElementException - if this is a Right.
 - isLeft
```
boolean isLeft()
```
 Returns whether this Either is a Left.
 
 Returns:
 
 true, if this is a Left, false otherwise
 - isRight
```
boolean isRight()
```
 Returns whether this Either is a Right.
 
 Returns:
 
 true, if this is a Right, false otherwise
 - left
```
@Deprecated
default Either.LeftProjection<L,R> left()
```
 Deprecated. Either is right-biased. Use swap() instead of projections.
 
 Returns a LeftProjection of this Either.
 
 Returns:
 
 a new LeftProjection of this
 - right
```
@Deprecated
default Either.RightProjection<L,R> right()
```
 Deprecated. Either is right-biased. Use swap() instead of projections.
 
 Returns a RightProjection of this Either.
 
 Returns:
 
 a new RightProjection of this
 - bimap
```
default <X,Y> Either<X,Y> bimap(Function<? super L,? extends X> leftMapper,
 Function<? super R,? extends Y> rightMapper)
```
 Maps either the left or the right side of this disjunction.
 
 Type Parameters:
 
 X - The new left type of the resulting Either
 
 Y - The new right type of the resulting Either
 
 Parameters:
 
 leftMapper - maps the left value if this is a Left
 
 rightMapper - maps the right value if this is a Right
 
 Returns:
 
 A new Either instance
 - fold
```
default  U fold(Function<? super L,? extends U> leftMapper,
 Function<? super R,? extends U> rightMapper)
```
 Folds either the left or the right side of this disjunction.
 
 Type Parameters:
 
 U - type of the folded value
 
 Parameters:
 
 leftMapper - maps the left value if this is a Left
 
 rightMapper - maps the right value if this is a Right
 
 Returns:
 
 A value of type U
 - sequence
```
static <L,R> Either<Seq<L>,Seq<R>> sequence(Iterable<? extends Either<? extends L,? extends R>> eithers)
```
 Reduces many Eithers into a single Either by transforming an Iterable<Either<L, R>> into a Either<Seq<L>, Seq<R>>.
 If any of the given Eithers is a Either.Left then sequence returns a Either.Left containing a non-empty Seq of all left values.
 If none of the given Eithers is a Either.Left then sequence returns a Either.Right containing a (possibly empty) Seq of all right values.
```
 // = Right(Seq())
 Either.sequence(List.empty())

 // = Right(Seq(1, 2))
 Either.sequence(List.of(Either.right(1), Either.right(2)))

 // = Left(Seq("x"))
 Either.sequence(List.of(Either.right(1), Either.left("x")))
 
```
 Type Parameters:
 
 L - closure of all left types of the given Eithers
 
 R - closure of all right types of the given Eithers
 
 Parameters:
 
 eithers - An Iterable of Eithers
 
 Returns:
 
 An Either of a Seq of left or right values
 
 Throws:
 
 NullPointerException - if eithers is null
 - traverse
```
static <L,R,T> Either<Seq<L>,Seq<R>> traverse(Iterable<? extends T> values,
 Function<? super T,? extends Either<? extends L,? extends R>> mapper)
```
 Maps the values of an iterable to a sequence of mapped values into a single Either by transforming an Iterable<? extends T> into a Either<Seq>.
 
 Type Parameters:
 
 L - The mapped left value type.
 
 R - The mapped right value type.
 
 T - The type of the given values.
 
 Parameters:
 
 values - An Iterable of values.
 
 mapper - A mapper of values to Eithers
 
 Returns:
 
 A Either of a Seq of results.
 
 Throws:
 
 NullPointerException - if values or f is null.
 - sequenceRight
```
static <L,R> Either<L,Seq<R>> sequenceRight(Iterable<? extends Either<? extends L,? extends R>> eithers)
```
 Reduces many Eithers into a single Either by transforming an Iterable<Either<L, R>> into a Either<L, Seq<R>>.
 If any of the given Eithers is a Either.Left then sequenceRight returns a Either.Left containing the first left value (in iteration order).
 If none of the given Eithers is a Either.Left then sequenceRight returns a Either.Right containing a (possibly empty) Seq of all right values.
```
 // = Right(Seq())
 Either.sequenceRight(List.empty())

 // = Right(Seq(1, 2))
 Either.sequenceRight(List.of(Either.right(1), Either.right(2)))

 // = Left("x1")
 Either.sequenceRight(List.of(Either.right(1), Either.left("x1"), Either.left("x2")))
 
```
 Type Parameters:
 
 L - closure of all left types of the given Eithers
 
 R - closure of all right types of the given Eithers
 
 Parameters:
 
 eithers - An Iterable of Eithers
 
 Returns:
 
 An Either of either a Seq of right values or the first left value, if present.
 
 Throws:
 
 NullPointerException - if eithers is null
 - traverseRight
```
static <L,R,T> Either<L,Seq<R>> traverseRight(Iterable<? extends T> values,
 Function<? super T,? extends Either<? extends L,? extends R>> mapper)
```
 Maps the values of an iterable to a sequence of mapped values into a single Either by transforming an Iterable<? extends T> into a Either<Seq>.
 
 Type Parameters:
 
 L - The mapped left value type.
 
 R - The mapped right value type.
 
 T - The type of the given values.
 
 Parameters:
 
 values - An Iterable of values.
 
 mapper - A mapper of values to Eithers
 
 Returns:
 
 A Either of a Seq of results.
 
 Throws:
 
 NullPointerException - if values or f is null.
 - getOrElseGet
```
default R getOrElseGet(Function<? super L,? extends R> other)
```
 Gets the Right value or an alternate value, if the projected Either is a Left.
 
 Parameters:
 
 other - a function which converts a Left value to an alternative Right value
 
 Returns:
 
 the right value, if the underlying Either is a Right or else the alternative Right value provided by other by applying the Left value.
 - orElseRun
```
default void orElseRun(Consumer<? super L> action)
```
 Runs an action in the case this is a projection on a Left value.
 
 Parameters:
 
 action - an action which consumes a Left value
 - getOrElseThrow
```
default <X extends Throwable> R getOrElseThrow(Function<? super L,X> exceptionFunction)
 throws X extends Throwable
```
 Gets the Right value or throws, if the projected Either is a Left.
 
 Type Parameters:
 
 X - a throwable type
 
 Parameters:
 
 exceptionFunction - a function which creates an exception based on a Left value
 
 Returns:
 
 the right value, if the underlying Either is a Right or else throws the exception provided by exceptionFunction by applying the Left value.
 
 Throws:
 
 X - if the projected Either is a Left
 
 X extends Throwable
 - swap
```
default Either<R,L> swap()
```
 Converts a Left to a Right vice versa by wrapping the value in a new type.
 
 Returns:
 
 a new Either
 - flatMap
```
default  Either<L,U> flatMap(Function<? super R,? extends Either<L,? extends U>> mapper)
```
 FlatMaps this right-biased Either.
 
 Type Parameters:
 
 U - Component type of the mapped right value
 
 Parameters:
 
 mapper - A mapper
 
 Returns:
 
 this as Either<L, U> if this is a Left, otherwise the right mapping result
 
 Throws:
 
 NullPointerException - if mapper is null
 - map
```
default  Either<L,U> map(Function<? super R,? extends U> mapper)
```
 Maps the value of this Either if it is a Right, performs no operation if this is a Left.
```
 import static io.vavr.API.*;

 // = Right("A")
 Right("a").map(String::toUpperCase);

 // = Left(1)
 Left(1).map(String::toUpperCase);
 
```
 Specified by:
 
 map in interface Value<R>
 
 Type Parameters:
 
 U - Component type of the mapped right value
 
 Parameters:
 
 mapper - A mapper
 
 Returns:
 
 a mapped Monad
 
 Throws:
 
 NullPointerException - if mapper is null
 - mapLeft
```
default  Either<U,R> mapLeft(Function<? super L,? extends U> leftMapper)
```
 Maps the value of this Either if it is a Left, performs no operation if this is a Right.
```
 import static io.vavr.API.*;

 // = Left(2)
 Left(1).mapLeft(i -> i + 1);

 // = Right("a")
 Right("a").mapLeft(i -> i + 1);
 
```
 Type Parameters:
 
 U - Component type of the mapped right value
 
 Parameters:
 
 leftMapper - A mapper
 
 Returns:
 
 a mapped Monad
 
 Throws:
 
 NullPointerException - if mapper is null
 - filter
```
default Option<Either<L,R>> filter(Predicate<? super R> predicate)
```
 Filters this right-biased Either by testing a predicate.
 
 Parameters:
 
 predicate - A predicate
 
 Returns:
 
 a new Option instance
 
 Throws:
 
 NullPointerException - if predicate is null
 - filterOrElse
```
default Either<L,R> filterOrElse(Predicate<? super R> predicate,
 Function<? super R,? extends L> zero)
```
 Filters this right-biased Either by testing a predicate. If the Either is a Right and the predicate doesn't match, the Either will be turned into a Left with contents computed by applying the filterVal function to the Either value.
```
 import static io.vavr.API.*;

 // = Left("bad: a")
 Right("a").filterOrElse(i -> false, val -> "bad: " + val);

 // = Right("a")
 Right("a").filterOrElse(i -> true, val -> "bad: " + val);
 
```
 Parameters:
 
 predicate - A predicate
 
 zero - A function that turns a right value into a left value if the right value does not make it through the filter.
 
 Returns:
 
 an Either instance
 
 Throws:
 
 NullPointerException - if predicate is null
 - get
```
R get()
```
 Gets the right value if this is a Right or throws if this is a Left.
 
 Specified by:
 
 get in interface Value<R>
 
 Returns:
 
 the right value
 
 Throws:
 
 NoSuchElementException - if this is a Left.
 - isEmpty
```
default boolean isEmpty()
```
 Description copied from interface: Value
 
 Checks, this Value is empty, i.e. if the underlying value is absent.
 
 Specified by:
 
 isEmpty in interface Value<R>
 
 Returns:
 
 false, if no underlying value is present, true otherwise.
 - orElse
```
default Either<L,R> orElse(Either<? extends L,? extends R> other)
```
 - orElse
```
default Either<L,R> orElse(Supplier<? extends Either<? extends L,? extends R>> supplier)
```
 - isAsync
```
default boolean isAsync()
```
 A right-biased Either's value is computed synchronously.
 
 Specified by:
 
 isAsync in interface Value<R>
 
 Returns:
 
 false
 - isLazy
```
default boolean isLazy()
```
 A right-biased Either's value is computed eagerly.
 
 Specified by:
 
 isLazy in interface Value<R>
 
 Returns:
 
 false
 - isSingleValued
```
default boolean isSingleValued()
```
 A right-biased Either is single-valued.
 
 Specified by:
 
 isSingleValued in interface Value<R>
 
 Returns:
 
 true
 - iterator
```
default Iterator<R> iterator()
```
 Description copied from interface: Value
 
 Returns a rich io.vavr.collection.Iterator.
 
 Specified by:
 
 iterator in interface Iterable<R>
 
 Specified by:
 
 iterator in interface Value<R>
 
 Returns:
 
 A new Iterator
 - peek
```
default Either<L,R> peek(Consumer<? super R> action)
```
 Description copied from interface: Value
 
 Performs the given action on the first element if this is an eager implementation. Performs the given action on all elements (the first immediately, successive deferred), if this is a lazy implementation.
 
 Specified by:
 
 peek in interface Value<R>
 
 Parameters:
 
 action - The action that will be performed on the element(s).
 
 Returns:
 
 this instance
 - peekLeft
```
default Either<L,R> peekLeft(Consumer<? super L> action)
```
 - toValidation
```
default Validation<L,R> toValidation()
```
 Returns this as Validation.
 
 Returns:
 
 Validation.valid(get()) if this is right, otherwise Validation.invalid(getLeft()).
 - equals
```
boolean equals(Object o)
```
 Description copied from interface: Value
 
 Clarifies that values have a proper equals() method implemented.
 See Object.equals(Object).
 
 Specified by:
 
 equals in interface Value<R>
 
 Overrides:
 
 equals in class Object
 
 Parameters:
 
 o - An object
 
 Returns:
 
 true, if this equals o, false otherwise
 - hashCode
```
int hashCode()
```
 Description copied from interface: Value
 
 Clarifies that values have a proper hashCode() method implemented.
 See Object.hashCode().
 
 Specified by:
 
 hashCode in interface Value<R>
 
 Overrides:
 
 hashCode in class Object
 
 Returns:
 
 The hashcode of this object
 - toString
```
String toString()
```
 Description copied from interface: Value
 
 Clarifies that values have a proper toString() method implemented.
 See Object.toString().
 
 Specified by:
 
 toString in interface Value<R>
 
 Overrides:
 
 toString in class Object
 
 Returns:
 
 A String representation of this object

Interface Either<L,R>

Nested Class Summary

Field Summary

Method Summary

Methods inherited from interface io.vavr.Value

Field Detail

serialVersionUID

Method Detail

right

left

narrow

getLeft

isLeft

isRight

left

right

bimap

fold

sequence

traverse

sequenceRight

traverseRight

getOrElseGet

orElseRun

getOrElseThrow

swap

flatMap

map

mapLeft

filter

filterOrElse

get

isEmpty

orElse

orElse

isAsync

isLazy

isSingleValued

iterator

peek

peekLeft

toValidation

equals

hashCode

toString