no.finntech.lambdacompanion

Class Either<L,R>

java.lang.Object

no.finntech.lambdacompanion.Either<L,R>

Type Parameters:

L - type of the left side

R - type of the right side

public abstract class Either<L,R>
extends Object

Represents a value of one of two possible types (a disjoint union.) Instances of Either are either an instance of Left or Right. A common use of Either is as an alternative to Optional for dealing with possible missing values. In this usage, Optional.Absent is replaced with a Left which can contain useful information. Right takes the place of Optional.Present. Convention dictates that Left is used for failure and Right is used for success.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Either.LeftProjection<L,R> Projects an Either into a Left.
static class	Either.RightProjection<L,R> Projects an Either into a Right.

Constructor Summary

Constructors

Constructor and Description
Either()

Method Summary

Modifier and Type	Method and Description
abstract boolean	equals(Object object) Returns true if this and object are both either a Left or a Right, and both their containing values are equal as determined by their equal methods.
abstract <X> X	fold(Function<L,X> leftMapper, Function<R,X> rightMapper) Applies leftMapper if this is a Left or rightMapper if this is a Right.
abstract int	hashCode()
abstract boolean	isLeft()
boolean	isRight()
abstract <X> Either<X,R>	joinLeft(Function<L,Either<X,R>> leftJoiner) Joins an Either through Left.
abstract <X> Either<L,X>	joinRight(Function<R,Either<L,X>> rightJoiner) Joins an Either through Right.
Either.LeftProjection<L,R>	left()
static <L,R> Either<L,R>	left(L value)
Either.RightProjection<L,R>	right()
static <L,R> Either<L,R>	right(R value)
abstract String	toString()

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Either

public Either()

Method Detail

isLeft

public abstract boolean isLeft()

Returns:

true if this is a Left, false otherwise.

isRight

public boolean isRight()

Returns:

true if this is a Right, false otherwise.

left

public Either.LeftProjection<L,R> left()

right

public Either.RightProjection<L,R> right()

equals

public abstract boolean equals(Object object)

Returns true if this and object are both either a Left or a Right, and both their containing values are equal as determined by their equal methods. Note that instances of differing parameterized types can be equal.

Overrides:

equals in class Object

hashCode

public abstract int hashCode()

Overrides:

hashCode in class Object

toString

public abstract String toString()

Overrides:

toString in class Object

fold

public abstract <X> X fold(Function<L,X> leftMapper,
                           Function<R,X> rightMapper)

Applies leftMapper if this is a Left or rightMapper if this is a Right.

Type Parameters:

X - the resulting type of applying the function

Parameters:

leftMapper - the function to apply if this is a Left

rightMapper - the function to apply if this is a Right

Returns:

the results of applying the function

joinLeft

public abstract <X> Either<X,R> joinLeft(Function<L,Either<X,R>> leftJoiner)

Joins an Either through Left. This method requires that the left side of this Either is itself an Either type. That is, this must be some type like: Either[Either[X, R], R] (which respects the type parameter bounds, shown below.) If this instance is a Left[Either[X, R]] then the contained Either[X, R] will be returned, otherwise this value will be returned unmodified.

Type Parameters:

X - the resulting type of applying the function

Parameters:

leftJoiner - the function to apply if this is a Left

Returns:

the results of applying the function

joinRight

public abstract <X> Either<L,X> joinRight(Function<R,Either<L,X>> rightJoiner)

Joins an Either through Right. This method requires that the right side of this Either is itself an Either type. That is, this must be some type like: Either[L, Either[L, X]] (which respects the type parameter bounds, shown below.) If this instance is a Right[Either[L, X]] then the contained Either[L, X] will be returned, otherwise this value will be returned unmodified.

Type Parameters:

X - the resulting type of applying the function

Parameters:

rightJoiner - the function to apply if this is a Right

Returns:

the results of applying the function

left

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

Type Parameters:

L - the type of the left side of the resulting Left[L,R]

R - the type of the right side of the resulting Left[L,R]

Parameters:

value - the value for the left side

Returns:

a Left of the given value

right

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

Type Parameters:

L - the type of the left side of the resulting Right[L,R]

R - the type of the right side of the resulting Right[L,R]

Parameters:

value - the value for the right side

Returns:

a Right of the given value