Add Before combinator

This commit is contained in:
Paul Campbell 2017-12-12 22:39:11 +00:00
parent 7a5f7a7632
commit d6ead54649
3 changed files with 140 additions and 0 deletions

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/**
* The MIT License (MIT)
*
* Copyright (c) 2017 Paul Campbell
*
* 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.
*/
package net.kemitix.mon.combinator;
import java.util.function.Consumer;
import java.util.function.Function;
/**
* Before pattern comninator.
*
* <p>Original from http://boundsofjava.com/newsletter/003-introducing-combinators-part1</p>
*
* @param <T> the argument type
* @param <R> the result type
*
* @author Federico Peralta Schaffner (fps@boundsofjava.com)
*/
@FunctionalInterface
public interface Before<T, R> extends
Function<
Consumer<T>,
Function<
Function<T, R>,
Function<T, R>>> {
/**
* Decorates a function with a Consumer that will be supplier with the argument before applying it to the function.
*
* @param before the consumer that will receive the argument before the function
* @param function the function to apply the argument to and return the result value of
* @param <T> the argument type
* @param <R> the result type
*
* @return a partially applied Function that will take an argument and return the result of applying it to the
* function parameter
*/
static <T, R> Function<T, R> decorate(
final Consumer<T> before,
final Function<T, R> function
) {
return Before.<T, R>create().apply(before)
.apply(function);
}
/**
* Create a Before curried function.
*
* @param <T> the argument type
* @param <R> the result type
*
* @return a curried function that will pass the argument to before applying the supplied function
*/
static <T, R> Before<T, R> create() {
return before -> function -> argument -> {
before.accept(argument);
return function.apply(argument);
};
}
}

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/**
* The MIT License (MIT)
*
* Copyright (c) 2017 Paul Campbell
*
* 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.
*/
package net.kemitix.mon.combinator;

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package net.kemitix.mon.combinator;
import org.junit.Test;
import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import static org.assertj.core.api.Assertions.assertThat;
public class BeforeTest {
@Test
public void canCreateBeforeCombinator() {
//given
final List<String> events = new ArrayList<>();
final Function<Integer, Integer> squareDecorated =
Before.decorate(v -> before(v, events), i -> function(i, events));
//when
final Integer result = squareDecorated.apply(2);
//then
assertThat(result).isEqualTo(4);
assertThat(events).containsExactly("before", "function");
}
private static void before(
final Integer v,
final List<String> events
) {
events.add("before");
}
private static Integer function(
final Integer i,
final List<String> events
) {
events.add("function");
return i * i;
}
}