com.atlassian.fugue

Class Either<L,R>

java.lang.Object

com.atlassian.fugue.Either<L,R>

public abstract class Either<L,R>
extends Object

A class that acts as a container for a value of one of two types. An Either will be either Left or Right.

Checking which type an Either is can be done by calling the @ isLeft() and isRight() methods.

An Either can be used to express a success or failure case. By convention, Right is used to store the success value, (you can use the play on words "right" == "correct" as a mnemonic) and Left is used to store failure values (such as exceptions).

While this class is public and abstract it does not expose a constructor as only the concrete Left and Right subclasses are meant to be used.

Either is immutable, but does not force immutability on contained objects; if the contained objects are mutable then equals and hashcode methods should not be relied on.

Since:

1.0

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	Either.LeftProjection A left projection of an either value.
static interface	Either.Projection<A,B,L,R>
class	Either.RightProjection A right projection of an either value.

Method Summary

Methods

Modifier and Type	Method and Description
static <L,R> Either<L,R>	cond(boolean predicate, R right, L left) Deprecated. in 1.2 use Eithers.cond(boolean, Object, Object)
abstract <V> V	fold(Function<? super L,V> ifLeft, Function<? super R,V> ifRight) Applies the function to the wrapped value, applying ifLeft it this is a Left and ifRight if this is a Right.
static <X extends Exception,A> A	getOrThrow(Either<X,A> either) Deprecated. in 1.2 use Eithers.getOrThrow(Either)
boolean	isLeft() Returns true if this either is a left, false otherwise.
boolean	isRight() Returns true if this either is a right, false otherwise.
Either.LeftProjection	left() Projects this either as a left.
static <L,R> Either<L,R>	left(L left)
static <T> T	merge(Either<T,T> either) Deprecated. in 1.2 use Eithers.merge(Either)
Either.RightProjection	right() Projects this either as a right.
static <L,R> Either<L,R>	right(R right)
static <L,R> Either<Iterable<L>,R>	sequenceLeft(Iterable<Either<L,R>> eithers) Deprecated. in 1.2 use Eithers.sequenceLeft(Iterable)
static <L,R> Either<L,Iterable<R>>	sequenceRight(Iterable<Either<L,R>> eithers) Deprecated. in 1.2 use Eithers.sequenceRight(Iterable)
abstract Either<R,L>	swap() If this is a left, then return the left value in right, or vice versa.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

left

public static <L,R> Either<L,R> left(L left)

Parameters:

left - the value to be stored, must not be null

Returns:

a Left containing the supplied value

right

public static <L,R> Either<L,R> right(R right)

Parameters:

right - the value to be stored, must not be null

Returns:

a Right containing the supplied value

merge

@Deprecated
public static <T> T merge(Either<T,T> either)

Deprecated. in 1.2 use Eithers.merge(Either)

cond

@Deprecated
public static <L,R> Either<L,R> cond(boolean predicate,
                                R right,
                                L left)

Deprecated. in 1.2 use Eithers.cond(boolean, Object, Object)

getOrThrow

@Deprecated
public static <X extends Exception,A> A getOrThrow(Either<X,A> either)
                    throws X extends Exception

Deprecated. in 1.2 use Eithers.getOrThrow(Either)

Throws:

X extends Exception

sequenceRight

@Deprecated
public static <L,R> Either<L,Iterable<R>> sequenceRight(Iterable<Either<L,R>> eithers)

Deprecated. in 1.2 use Eithers.sequenceRight(Iterable)

sequenceLeft

@Deprecated
public static <L,R> Either<Iterable<L>,R> sequenceLeft(Iterable<Either<L,R>> eithers)

Deprecated. in 1.2 use Eithers.sequenceLeft(Iterable)

isLeft

public boolean isLeft()

Returns true if this either is a left, false otherwise.

Returns:

true if this either is a left, false otherwise.

isRight

public boolean isRight()

Returns true if this either is a right, false otherwise.

Returns:

true if this either is a right, false otherwise.

left

public final Either.LeftProjection left()

Projects this either as a left.

Returns:

A left projection of this either.

right

public final Either.RightProjection right()

Projects this either as a right.

Returns:

A right projection of this either.

swap

public abstract Either<R,L> swap()

If this is a left, then return the left value in right, or vice versa.

Returns:

an Either that is a Left if this is a Right or a Right if this is a Left. The value remains the same.

fold

public abstract <V> V fold(Function<? super L,V> ifLeft,
         Function<? super R,V> ifRight)

Applies the function to the wrapped value, applying ifLeft it this is a Left and ifRight if this is a Right.

Parameters:

ifLeft - the function to apply if this is a Left

ifRight - the function to apply if this is a Right

Returns:

the result of the applies function