org.opencastproject.util.data

Class Option<A>

java.lang.Object

org.opencastproject.util.data.Option<A>

All Implemented Interfaces:

Iterable<A>

public abstract class Option<A>
extends Object
implements Iterable<A>

The option type encapsulates on optional value. It contains either some value or is empty. Please make sure to NEVER wrap null into a some. Instead use none.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Option.EMatch<A> Effect match.
static interface	Option.Match<A,B>

Method Summary

Modifier and Type	Method and Description
<B> Option<Tuple<A,B>>	and(Option<B> b)
<B> Option<B>	andThen(Function0<Option<B>> some) Lazy version of andThen(Option).
<B> Option<B>	andThen(Option<B> some) If this is some return some.
<B> Option<B>	andThenV(B some) If this is some return some.
<B> Option<B>	andThenV(Function0<B> some) Lazy version of andThenV(Object).
abstract <B> Option<B>	bind(Function<A,Option<B>> f) Monadic bind operation m a -> (a -> m b) -> m b.
static Function<String,Boolean>	eq(String compare) Create an equals function.
abstract boolean	equals(Object o)
static <A> Function0<A>	error(String message) Deprecated. use orError(Throwable) or orElse(Function0) instead since it saves the need for creating new objects just for the sake of type soundness. Java unfortunately lacks a bottom type.
<B> Option<B>	flatMap(Function<A,Option<B>> f)
abstract <B> Option<B>	fmap(Function<? super A,? extends B> f)
<B> B	fold(Function<A,B> some, Function0<B> none) Safe decomposition of the option type using functions.
abstract <B> B	fold(Option.Match<A,B> visitor) Safe decomposition of the option type.
abstract Option<A>	foreach(Function<? super A,Void> f)
static <A> Option<A>	fromOpt(com.entwinemedia.fn.data.Opt<A> a) Convert an Opt into an Option.
abstract A	get() Get the contained value or throw an exception.
abstract A	getOrElse(A none) Get the contained value in case of being "some" or return parameter none otherwise.
abstract A	getOrElse(Function0<A> none) Get the contained value in case of being "some" or return the result of evaluating none otherwise.
abstract A	getOrElseNull() To interface with legacy applications or frameworks that still use null values.
abstract int	hashCode()
Option<A>	inv(A zero) Inversion.
boolean	isNone()
abstract boolean	isSome()
abstract <B> Either<A,B>	left(B right) Left projection of this option.
abstract List<A>	list() Transform an option into a list, either with a single element or an empty list.
<B> Option<B>	map(Function<? super A,? extends B> f)
abstract Monadics.ListMonadic<A>	mlist() Transform the option into a monadic list.
static <A> Option<A>	none() Create a new none.
static <A> Option<A>	none(A example) Create a none with the type of example.
static <A> Option<A>	none(Class<A> clazz) Create a none with the given type.
static <A> Function<A,Option<A>>	option() option(Object) as a function.
static <A> Option<A>	option(A a) Wrap an arbitrary object into an option with null being mapped to none.
Option<A>	orElse(Function0<Option<A>> none) Lazy version of orElse(Option).
Option<A>	orElse(Option<A> none) If this is none return none else this.
<T extends Throwable> Option<A>	orError(Class<T> none) Throw none if none.
<T extends Throwable> Option<A>	orError(Function0<T> none) Throw exception returned by none if none.
<T extends Throwable> Option<A>	orError(T none) Throw none if none.
abstract <B> Either<B,A>	right(B left) Right projection of this optio.
static <A> Option<A>	some(A a) Create a new some.
abstract com.entwinemedia.fn.data.Opt<A>	toOpt()

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.lang.Iterable

forEach, iterator, spliterator

Method Detail

fold

public abstract <B> B fold(Option.Match<A,B> visitor)

Safe decomposition of the option type.

fold

public <B> B fold(Function<A,B> some,
                  Function0<B> none)

Safe decomposition of the option type using functions.

foreach

public abstract Option<A> foreach(Function<? super A,Void> f)

fmap

public abstract <B> Option<B> fmap(Function<? super A,? extends B> f)

map

public <B> Option<B> map(Function<? super A,? extends B> f)

bind

public abstract <B> Option<B> bind(Function<A,Option<B>> f)

Monadic bind operation m a -> (a -> m b) -> m b.

flatMap

public <B> Option<B> flatMap(Function<A,Option<B>> f)

See Also:

Functions.bind(Function)

isSome

public abstract boolean isSome()

isNone

public boolean isNone()

andThen

public <B> Option<B> andThen(Option<B> some)

If this is some return some. Like bind(Function) but ignores the option's content.

andThenV

public <B> Option<B> andThenV(B some)

If this is some return some. Like map(Function) but ignores the option's content.

andThen

public <B> Option<B> andThen(Function0<Option<B>> some)

Lazy version of andThen(Option).

andThenV

public <B> Option<B> andThenV(Function0<B> some)

Lazy version of andThenV(Object).

orElse

public Option<A> orElse(Option<A> none)

If this is none return none else this.

orElse

public Option<A> orElse(Function0<Option<A>> none)

Lazy version of orElse(Option).

orError

public <T extends Throwable> Option<A> orError(T none)
                                        throws T extends Throwable

Throw none if none.

Throws:

T extends Throwable

orError

public <T extends Throwable> Option<A> orError(Class<T> none)
                                        throws T extends Throwable

Throw none if none.

Throws:

T extends Throwable

orError

public <T extends Throwable> Option<A> orError(Function0<T> none)
                                        throws T extends Throwable

Throw exception returned by none if none.

Throws:

T extends Throwable

and

public <B> Option<Tuple<A,B>> and(Option<B> b)

get

public abstract A get()

Get the contained value or throw an exception.

getOrElse

public abstract A getOrElse(A none)

Get the contained value in case of being "some" or return parameter none otherwise.

getOrElse

public abstract A getOrElse(Function0<A> none)

Get the contained value in case of being "some" or return the result of evaluating none otherwise.

getOrElseNull

public abstract A getOrElseNull()

To interface with legacy applications or frameworks that still use null values.

mlist

public abstract Monadics.ListMonadic<A> mlist()

Transform the option into a monadic list.

list

public abstract List<A> list()

Transform an option into a list, either with a single element or an empty list.

left

public abstract <B> Either<A,B> left(B right)

Left projection of this option. If the option is some return the value in an Either.left(Object) else return right in an Either.right(Object).

right

public abstract <B> Either<B,A> right(B left)

Right projection of this optio. If the option is some return the value in an Either.left(Object) else return right in an Either.right(Object).

toOpt

public abstract com.entwinemedia.fn.data.Opt<A> toOpt()

inv

public Option<A> inv(A zero)

Inversion. If some return none. If none return some(zero).

hashCode

public abstract int hashCode()

Overrides:

hashCode in class Object

equals

public abstract boolean equals(Object o)

Overrides:

equals in class Object

some

public static <A> Option<A> some(A a)

Create a new some.

none

public static <A> Option<A> none()

Create a new none.

none

public static <A> Option<A> none(A example)

Create a none with the type of example. This saves some nasty typing, e.g. Option.<String>none() vs. none("").

Please note that this constructor is only due to Java's insufficient type inference.

none

public static <A> Option<A> none(Class<A> clazz)

Create a none with the given type.

option

public static <A> Option<A> option(A a)

Wrap an arbitrary object into an option with null being mapped to none.

fromOpt

public static <A> Option<A> fromOpt(com.entwinemedia.fn.data.Opt<A> a)

Convert an Opt into an Option.

option

public static <A> Function<A,Option<A>> option()

option(Object) as a function.

error

@Deprecated
public static <A> Function0<A> error(String message)

Deprecated. use orError(Throwable) or orElse(Function0) instead since it saves the need for creating new objects just for the sake of type soundness. Java unfortunately lacks a bottom type.

Use this function in getOrElse if it is an error being none.

eq

public static Function<String,Boolean> eq(String compare)

Create an equals function.

   some("abc").map(eq("bcd")).getOrElse(false) // false
   some("abc").map(eq("abc")).getOrElse(false) // true