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// Copyright (c) 2003-present, Jodd Team (http://jodd.org)
// All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:
//
// 1. Redistributions of source code must retain the above copyright notice,
// this list of conditions and the following disclaimer.
//
// 2. Redistributions in binary form must reproduce the above copyright
// notice, this list of conditions and the following disclaimer in the
// documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
// AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
// SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
// CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
// ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.
package jodd.util.function;
import java.util.Collections;
import java.util.Iterator;
import java.util.Objects;
import java.util.Optional;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;
import java.util.stream.Stream;
/**
* Slightly better Maybe monad. It does not have a {@code get()}, but it has {@code or()} :).
* Slightly better implementation of Optional, as there are no IF blocks all over the class.
*/
public interface Maybe extends Iterable {
/**
* Static factory for Maybe.
*/
static Maybe of(final T value) {
if (value == null) {
return nothing();
}
return just(value);
}
@SuppressWarnings("OptionalUsedAsFieldOrParameterType")
static Maybe of(final Optional optionalValue) {
return optionalValue.map(Maybe::of).orElseGet(Maybe::nothing);
}
/**
* Returns {@code true} if value is present.
*/
boolean isJust();
/**
* Returns {@code false} if value is not present.
*/
boolean isNothing();
/**
* Takes a default value and a function. If the Maybe value is Nothing, the function returns the default value.
* Otherwise, it applies the function to the value inside the Just and returns the result.
*/
V maybe(V defaultValue, Function function);
/**
* Consumes value if present.
*/
void consumeJust(Consumer consumer);
/**
* Returns empty or single-element stream.
*/
Stream stream();
/**
* Use a maybe of given value if this one is NOTHING.
*/
Maybe or(T otherValue);
/**
* Use give maybe if this one is NOTHING.
*/
Maybe or(Maybe maybe);
/**
* Use supplied value if this one is NOTHING.
*/
Maybe or(Supplier> supplier);
/**
* Map.
*/
Maybe map(Function mapper);
/**
* Flat map.
*/
Maybe flatMap(Function> mapper);
Maybe filter(Predicate mapping);
/**
* Converts Maybe to the Java Optional.
*/
Optional optional();
/**
* Returns a NOTHING.
*/
static Maybe nothing() {
return new Maybe() {
@Override
public boolean isJust() {
return false;
}
@Override
public boolean isNothing() {
return true;
}
@Override
public V maybe(final V defaultValue, final Function function) {
return defaultValue;
}
@Override
public void consumeJust(final Consumer consumer) {
}
@Override
public Iterator iterator() {
return Collections.emptyList().iterator();
}
@Override
public Stream stream() {
return Stream.empty();
}
@Override
public Maybe or(final T otherValue) {
return Maybe.of(otherValue);
}
@Override
public Maybe or(final Maybe maybeJust) {
return maybeJust;
}
@SuppressWarnings("unchecked")
@Override
public Maybe or(final Supplier> supplier) {
final Maybe r = (Maybe) supplier.get();
return Objects.requireNonNull(r);
}
@Override
public Maybe map(final Function mapper) {
return nothing();
}
@Override
public Maybe flatMap(final Function> mapper) {
return nothing();
}
@Override
public Maybe filter(final Predicate mapping) {
return nothing();
}
@Override
public String toString() {
return "nothing";
}
@Override
public boolean equals(final Object obj) {
return false;
}
@Override
public int hashCode() {
return 0;
}
@Override
public Optional optional() {
return Optional.empty();
}
};
}
/**
* Returns a JUST>
*/
static Maybe just(final T theValue) {
return new Just<>(theValue);
}
class Just implements Maybe {
private final T value;
private Just(final T value) {
Objects.requireNonNull(value);
this.value = value;
}
@Override
public boolean isJust() {
return true;
}
@Override
public boolean isNothing() {
return false;
}
@Override
public V maybe(final V defaultValue, final Function function) {
return function.apply(value);
}
@Override
public void consumeJust(final Consumer consumer) {
consumer.accept(value);
}
@Override
public Iterator iterator() {
return Collections.singleton(value).iterator();
}
@Override
public Stream stream() {
return Stream.of(value);
}
@Override
public Maybe or(final T otherValue) {
return this;
}
@Override
public Maybe or(final Maybe maybeDefaultValue) {
return this;
}
@Override
public Maybe or(final Supplier> supplier) {
return this;
}
@Override
public Maybe map(final Function mapper) {
return Maybe.of(mapper.apply(value));
}
@Override
public Maybe flatMap(final Function> mapper) {
return mapper.apply(value);
}
@Override
public Maybe filter(final Predicate predicate) {
return predicate.test(value) ? this : nothing();
}
@Override
public String toString() {
return "just: " + value.toString();
}
@Override
public boolean equals(final Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
final Just that = (Just) o;
return value.equals(that.value);
}
@Override
public int hashCode() {
return value.hashCode();
}
@Override
public Optional optional() {
return Optional.of(value);
}
}
}