Add Around combinator
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101
src/main/java/net/kemitix/mon/combinator/Around.java
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101
src/main/java/net/kemitix/mon/combinator/Around.java
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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.combinator;
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import java.util.concurrent.atomic.AtomicReference;
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import java.util.function.BiConsumer;
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import java.util.function.Function;
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/**
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* Around pattern combinator.
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*
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* <p>Original from http://boundsofjava.com/newsletter/003-introducing-combinators-part1</p>
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*
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* @param <T> the argument type
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* @param <R> the result type
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*
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* @author Federico Peralta Schaffner (fps@boundsofjava.com)
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*/
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@FunctionalInterface
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public interface Around<T, R> extends
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Function<
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Function<T, R>,
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Function<
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BiConsumer<Around.Executable<R>, T>,
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Function<T, R>>> {
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/**
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* Decorates a function with an BiConsumer that will be supplier with an executable to perform the function, and the
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* argument that will be applied when executed.
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*
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* @param function the function to apply the argument to and return the result value of
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* @param around the bi-consumer that will supplied with the executable and the argument
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* @param <T> the argument type
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* @param <R> the result type
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*
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* @return a partially applied Function that will take an argument, and the result of applying it to function
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*/
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static <T, R> Function<T, R> decorate(
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final Function<T, R> function,
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final BiConsumer<Executable<R>, T> around
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) {
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return Around.<T, R>create().apply(function)
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.apply(around);
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}
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/**
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* Create an Around curried function.
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*
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* @param <T> the argument type
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* @param <R> the result type
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*
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* @return a curried function that will execute the around function, passing an executable and the invocations
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* argument. The around function must {@code execute()} the executable and may capture the result.
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*/
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static <T, R> Around<T, R> create() {
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return function -> around -> argument -> {
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final AtomicReference<R> result = new AtomicReference<>();
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final Executable<R> callback = () -> {
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result.set(function.apply(argument));
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return result.get();
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};
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around.accept(callback, argument);
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return result.get();
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};
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}
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/**
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* The executable that will be supplied to the around function to trigger the surrounded function.
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*
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* @param <R> the return type of the function
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*/
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@FunctionalInterface
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interface Executable<R> {
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/**
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* Executes the function.
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*
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* @return the result of applying the function
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*/
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R execute();
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}
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}
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@ -16,7 +16,6 @@ public class AfterTest {
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final List<String> events = new ArrayList<>();
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final Function<Integer, Integer> squareDecorated =
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After.decorate(i -> function(i, events), (v, r) -> after(v, r, events));
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//when
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final Integer result = squareDecorated.apply(2);
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//then
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46
src/test/java/net/kemitix/mon/combinator/AroundTest.java
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src/test/java/net/kemitix/mon/combinator/AroundTest.java
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package net.kemitix.mon.combinator;
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import org.junit.Test;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.function.Function;
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import static org.assertj.core.api.Assertions.assertThat;
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public class AroundTest {
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@Test
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public void canCreateAnAroundCombinator() {
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//given
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final List<String> events = new ArrayList<>();
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final Function<Integer, Integer> squareDecorated =
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Around.decorate(
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i -> function(i, events),
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(executable, argument) -> around(executable, argument, events)
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);
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//when
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final Integer result = squareDecorated.apply(2);
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//then
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assertThat(result).isEqualTo(4);
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assertThat(events).containsExactly("around before 2", "function", "around after 4");
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}
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private void around(
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final Around.Executable<Integer> executable,
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final Integer argument,
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final List<String> events
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) {
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events.add("around before " + argument);
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final Integer result = executable.execute();
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events.add("around after " + result);
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}
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private static Integer function(
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final Integer argument,
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final List<String> events
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) {
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events.add("function");
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return argument * argument;
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}
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}
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