commit
1ffb5536d0
9 changed files with 469 additions and 5 deletions
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@ -5,6 +5,7 @@ CHANGELOG
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-----
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* Restore public access for `TypeAlias.getValue()`
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* Add `Maybe`, `Just`, `Nothing`
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0.3.0
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-----
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34
README.md
34
README.md
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@ -41,3 +41,37 @@ void foo(final Goal goal) {
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System.out.println("The goal is " + goal.getValue());
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}
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```
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### Maybe (Just & Nothing)
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```java
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assertThat(Maybe.maybe(null)).isEqualTo(Maybe.nothing());
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assertThat(Maybe.maybe(1)).isEqualTo(Maybe.just(1));
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assertThat(Maybe.nothing()
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.orElseGet(() -> 1)).isEqualTo(1);
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assertThat(Maybe.just(1)
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.orElseGet(() -> 2)).isEqualTo(1);
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assertThat(Maybe.nothing()
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.orElse(1)).isEqualTo(1);
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assertThat(Maybe.just(1)
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.orElse(2)).isEqualTo(1);
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assertThat(Maybe.just(1)
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.filter(v -> v > 2)).isEqualTo(Maybe.nothing());
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assertThat(Maybe.just(3)
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.filter(v -> v > 2)).isEqualTo(Maybe.just(3));
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assertThat(Maybe.just(1)
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.toOptional()).isEqualTo(Optional.of(1));
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assertThat(Maybe.nothing()
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.toOptional()).isEqualTo(Optional.empty());
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assertThat(Maybe.fromOptional(Optional.of(1))).isEqualTo(Maybe.just(1));
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assertThat(Maybe.fromOptional(Optional.empty())).isEqualTo(Maybe.nothing());
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final AtomicInteger reference = new AtomicInteger(0);
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assertThat(Maybe.just(1).peek(reference::set)).isEqualTo(Maybe.just(1));
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assertThat(reference).hasValue(1);
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assertThat(Maybe.nothing().peek(v -> reference.incrementAndGet())).isEqualTo(Maybe.nothing());
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assertThat(reference).hasValue(1);
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assertThatCode(() -> Maybe.just(1).orElseThrow(IllegalStateException::new))
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.doesNotThrowAnyException();
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assertThatThrownBy(() -> Maybe.nothing().orElseThrow(IllegalStateException::new))
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.isInstanceOf(IllegalStateException.class);
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```
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@ -34,18 +34,19 @@ import java.util.function.Function;
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* </ul>
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*
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* @param <T> the type of the Functor
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* @param <F> the type of the mapped Functor
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*
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* @author Tomasz Nurkiewicz (?@?.?)
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*/
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public interface Functor<T> {
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public interface Functor<T, F extends Functor<?, ?>> {
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/**
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* Applies the function to the value within the Functor, returning the result within a Functor.
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*
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* @param f the function to apply
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* @param <R> the type of the result of the function
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* @param <R> the type of the content of the mapped functor
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*
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* @return a Functor containing the result of the function {@code f} applied to the value
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*/
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<R> Functor<R> map(Function<T, R> f);
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<R> F map(Function<T, R> f);
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}
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@ -33,7 +33,7 @@ import java.util.function.Function;
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* @author Paul Campbell (pcampbell@kemitix.net)
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*/
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@RequiredArgsConstructor
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class Identity<T> implements Functor<T> {
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class Identity<T> implements Functor<T, Identity<?>> {
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private final T value;
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94
src/main/java/net/kemitix/mon/Just.java
Normal file
94
src/main/java/net/kemitix/mon/Just.java
Normal file
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@ -0,0 +1,94 @@
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/**
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* The MIT License (MIT)
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*
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* Copyright (c) 2017 Paul Campbell
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this software
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* and associated documentation files (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
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* subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies
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* or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
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* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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* AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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package net.kemitix.mon;
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import lombok.AccessLevel;
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import lombok.RequiredArgsConstructor;
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import java.util.Objects;
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import java.util.Optional;
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import java.util.function.Consumer;
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import java.util.function.Function;
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import java.util.function.Predicate;
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import java.util.function.Supplier;
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/**
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* A Maybe where a value is present.
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*
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* @param <T> the type of the content
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*
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* @author Paul Campbell (pcampbell@kemitix.net)
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*/
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@RequiredArgsConstructor(access = AccessLevel.PROTECTED)
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public final class Just<T> implements Maybe<T> {
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private final T value;
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@Override
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public <R> Maybe<?> map(final Function<T, R> f) {
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return new Just<>(f.apply(value));
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}
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@Override
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public boolean equals(final Object other) {
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return other instanceof Just && Objects.equals(this.value, ((Just) other).value);
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}
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@Override
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public int hashCode() {
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return Objects.hashCode(value);
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}
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@Override
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public T orElseGet(final Supplier<T> supplier) {
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return value;
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}
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@Override
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public T orElse(final T otherValue) {
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return this.value;
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}
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@Override
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public Maybe<T> filter(final Predicate<T> predicate) {
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if (predicate.test(value)) {
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return this;
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}
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return Maybe.nothing();
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}
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@Override
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public Optional<T> toOptional() {
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return Optional.of(value);
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}
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@Override
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public Maybe<T> peek(final Consumer<T> consumer) {
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consumer.accept(value);
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return this;
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}
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@Override
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public void orElseThrow(final Supplier<Exception> e) {
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// do not throw
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}
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}
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145
src/main/java/net/kemitix/mon/Maybe.java
Normal file
145
src/main/java/net/kemitix/mon/Maybe.java
Normal file
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@ -0,0 +1,145 @@
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/**
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* The MIT License (MIT)
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*
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* Copyright (c) 2017 Paul Campbell
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy of this software
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* and associated documentation files (the "Software"), to deal in the Software without restriction,
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* including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
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* and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
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* subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all copies
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* or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
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* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
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* AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
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* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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*/
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package net.kemitix.mon;
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import lombok.NonNull;
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import java.util.Optional;
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import java.util.function.Consumer;
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import java.util.function.Predicate;
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import java.util.function.Supplier;
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/**
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* A value that may or may not be present.
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*
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* @param <T> the type of the content of the Just
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*
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* @author Paul Campbell (pcampbell@kemitix.net)
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*/
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public interface Maybe<T> extends Functor<T, Maybe<?>> {
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/**
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* Create a Maybe for the value that is present.
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*
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* @param value the value, not null
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* @param <T> the type of the value
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*
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* @return a Maybe of the value
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*/
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static <T> Maybe<T> just(@NonNull final T value) {
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return new Just<>(value);
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}
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/**
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* Create a Maybe for a lack of a value.
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*
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* @param <T> the type of the missing value
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*
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* @return an empty Maybe
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*/
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@SuppressWarnings("unchecked")
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static <T> Maybe<T> nothing() {
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return (Maybe<T>) Nothing.INSTANCE;
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}
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/**
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* Create a Maybe for the value that may or may not be present.
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*
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* @param value the value, may be null
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* @param <T> the type of the value
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*
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* @return a Maybe, either a Just, or Nothing if value is null
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*/
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static <T> Maybe<T> maybe(final T value) {
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if (value == null) {
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return nothing();
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}
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return just(value);
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}
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/**
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* Create a Maybe from an {@link Optional}.
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*
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* @param optional the Optional
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* @param <T> the type of the Optional
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*
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* @return a Maybe
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*/
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static <T> Maybe<T> fromOptional(final Optional<T> optional) {
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return optional.map(Maybe::maybe)
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.orElse(nothing());
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}
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/**
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* Provide a value to use when Maybe is Nothing.
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*
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* @param supplier supplier for an alternate value
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*
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* @return a Maybe
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*/
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T orElseGet(Supplier<T> supplier);
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/**
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* A value to use when Maybe is Nothing.
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*
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* @param otherValue an alternate value
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*
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* @return a Maybe
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*/
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T orElse(T otherValue);
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/**
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* Filter a Maybe by the predicate, replacing with Nothing when it fails.
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*
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* @param predicate the test
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*
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* @return the Maybe, or Nothing if the test returns false
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*/
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Maybe<T> filter(Predicate<T> predicate);
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/**
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* Convert the Maybe to an {@link Optional}.
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*
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* @return an Optional containing a value for a Just, or empty for a Nothing
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*/
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Optional<T> toOptional();
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/**
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* Provide the value within the Maybe, if it exists, to the Supplier, and returns the Maybe.
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*
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* @param consumer the Consumer to the value if present
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*
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* @return the Maybe
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*/
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Maybe<T> peek(Consumer<T> consumer);
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/**
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* Throw the exception if the Maybe is a Nothing.
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*
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* @param e the exception to throw
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*
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* @throws Exception if the Maybe is a Nothing
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*/
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@SuppressWarnings("illegalthrows")
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void orElseThrow(Supplier<Exception> e) throws Exception;
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}
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@ -37,7 +37,7 @@ import java.util.function.Supplier;
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* @author Paul Campbell (pcampbell@kemitix.net)
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*/
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@RequiredArgsConstructor(access = AccessLevel.PROTECTED)
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public class Mon<T> implements Functor<T> {
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public class Mon<T> implements Functor<T, Mon<?>> {
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/**
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* The value.
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|
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75
src/main/java/net/kemitix/mon/Nothing.java
Normal file
75
src/main/java/net/kemitix/mon/Nothing.java
Normal file
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@ -0,0 +1,75 @@
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/**
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* The MIT License (MIT)
|
||||
*
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* Copyright (c) 2017 Paul Campbell
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*
|
||||
* Permission is hereby granted, free of charge, to any person obtaining a copy of this software
|
||||
* and associated documentation files (the "Software"), to deal in the Software without restriction,
|
||||
* including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense,
|
||||
* and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so,
|
||||
* subject to the following conditions:
|
||||
*
|
||||
* The above copyright notice and this permission notice shall be included in all copies
|
||||
* or substantial portions of the Software.
|
||||
*
|
||||
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
|
||||
* INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
|
||||
* AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM,
|
||||
* DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
|
||||
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
|
||||
*/
|
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|
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package net.kemitix.mon;
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import java.util.Optional;
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import java.util.function.Consumer;
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import java.util.function.Function;
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import java.util.function.Predicate;
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import java.util.function.Supplier;
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/**
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* A Maybe where no value is present.
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*
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* @param <T> the type of the missing content
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*
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* @author Paul Campbell (pcampbell@kemitix.net)
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*/
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public final class Nothing<T> implements Maybe<T> {
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protected static final Maybe<?> INSTANCE = new Nothing<>();
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@Override
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public <R> Maybe<?> map(final Function<T, R> f) {
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return this;
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}
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@Override
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public T orElseGet(final Supplier<T> supplier) {
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return supplier.get();
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}
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|
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@Override
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public T orElse(final T otherValue) {
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return otherValue;
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}
|
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|
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@Override
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public Maybe<T> filter(final Predicate<T> predicate) {
|
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return this;
|
||||
}
|
||||
|
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@Override
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||||
public Optional<T> toOptional() {
|
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return Optional.empty();
|
||||
}
|
||||
|
||||
@Override
|
||||
public Maybe<T> peek(final Consumer<T> consumer) {
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return this;
|
||||
}
|
||||
|
||||
@Override
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||||
public void orElseThrow(final Supplier<Exception> e) throws Exception {
|
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throw e.get();
|
||||
}
|
||||
}
|
114
src/test/java/net/kemitix/mon/MaybeTest.java
Normal file
114
src/test/java/net/kemitix/mon/MaybeTest.java
Normal file
|
@ -0,0 +1,114 @@
|
|||
package net.kemitix.mon;
|
||||
|
||||
import org.junit.Test;
|
||||
|
||||
import java.util.Objects;
|
||||
import java.util.Optional;
|
||||
import java.util.concurrent.atomic.AtomicInteger;
|
||||
import java.util.function.Predicate;
|
||||
|
||||
import static net.kemitix.mon.Maybe.just;
|
||||
import static net.kemitix.mon.Maybe.maybe;
|
||||
import static net.kemitix.mon.Maybe.nothing;
|
||||
import static org.assertj.core.api.Assertions.assertThat;
|
||||
import static org.assertj.core.api.Assertions.assertThatCode;
|
||||
import static org.assertj.core.api.Assertions.assertThatNullPointerException;
|
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import static org.assertj.core.api.Assertions.assertThatThrownBy;
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|
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public class MaybeTest {
|
||||
|
||||
private static <T> Predicate<T> eq(final T value) {
|
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return v -> Objects.equals(value, v);
|
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}
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||||
|
||||
@Test
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public void justMustBeNonNull() {
|
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assertThatNullPointerException().isThrownBy(() -> just(null))
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.withMessage("value");
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}
|
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|
||||
@Test
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||||
public void nothingReusesTheSameInstance() {
|
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assertThat(nothing()).isSameAs(nothing());
|
||||
}
|
||||
|
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@Test
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||||
public void equality() {
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||||
assertThat(just(1)).isEqualTo(just(1));
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assertThat(just(1)).isNotEqualTo(just(2));
|
||||
assertThat(just(1)).isNotEqualTo(nothing());
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||||
assertThat(nothing()).isEqualTo(nothing());
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assertThat(just(1).equals("1")).isFalse();
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||||
}
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||||
|
||||
@Test
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||||
public void maybeAllowsNull() {
|
||||
assertThat(just(1)).isEqualTo(maybe(1));
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||||
assertThat(nothing()).isEqualTo(maybe(null));
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||||
}
|
||||
|
||||
@Test
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||||
public void map() {
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||||
assertThat(just(1).map(v -> v + 1)).isEqualTo(just(2));
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assertThat(nothing().map(v -> v)).isEqualTo(nothing());
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||||
}
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||||
|
||||
@Test
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||||
public void testHashCode() {
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||||
assertThat(just(1).hashCode()).isEqualTo(Objects.hashCode(1));
|
||||
}
|
||||
|
||||
@Test
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||||
public void orElseGet() {
|
||||
assertThat(just(1).orElseGet(() -> -1)).isEqualTo(1);
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||||
assertThat(nothing().orElseGet(() -> -1)).isEqualTo(-1);
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||||
}
|
||||
|
||||
@Test
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||||
public void orElse() {
|
||||
assertThat(just(1).orElse(-1)).isEqualTo(1);
|
||||
assertThat(nothing().orElse(-1)).isEqualTo(-1);
|
||||
}
|
||||
|
||||
@Test
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||||
public void filter() {
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||||
assertThat(just(1).filter(eq(1))).isEqualTo(just(1));
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||||
assertThat(just(1).filter(eq(0))).isEqualTo(nothing());
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||||
assertThat(nothing().filter(eq(1))).isEqualTo(nothing());
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||||
}
|
||||
|
||||
@Test
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||||
public void toOptional() {
|
||||
assertThat(just(1).toOptional()).isEqualTo(Optional.of(1));
|
||||
assertThat(nothing()
|
||||
.toOptional()).isEqualTo(Optional.empty());
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||||
}
|
||||
|
||||
@Test
|
||||
public void fromOptional() {
|
||||
assertThat(Maybe.fromOptional(Optional.of(1))).isEqualTo(just(1));
|
||||
assertThat(Maybe.fromOptional(Optional.empty())).isEqualTo(nothing());
|
||||
}
|
||||
|
||||
|
||||
@Test
|
||||
public void peek() {
|
||||
final AtomicInteger ref = new AtomicInteger(0);
|
||||
assertThat(just(1).peek(x -> ref.incrementAndGet())).isEqualTo(just(1));
|
||||
assertThat(ref.get()).isEqualTo(1);
|
||||
|
||||
assertThat(nothing().peek(x -> ref.incrementAndGet())).isEqualTo(nothing());
|
||||
assertThat(ref.get()).isEqualTo(1);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void justOrThrow() {
|
||||
assertThatCode(() -> just(1).orElseThrow(IllegalStateException::new)).doesNotThrowAnyException();
|
||||
}
|
||||
|
||||
@Test
|
||||
public void nothingOrThrow() {
|
||||
assertThatThrownBy(() -> nothing().orElseThrow(IllegalStateException::new)).isInstanceOf(
|
||||
IllegalStateException.class);
|
||||
}
|
||||
}
|
Loading…
Reference in a new issue