200 lines
7.3 KiB
Markdown
200 lines
7.3 KiB
Markdown
Mon
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===
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TypeAlias, Maybe and Result for Java
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[](https://oss.sonatype.org/content/repositories/releases/net/kemitix/mon/)
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[](https://search.maven.org/#search|ga|1|g%3A"net.kemitix"%20AND%20a%3A"mon")
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[](https://sonarcloud.io/dashboard?id=net.kemitix%3Amon)
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[](https://sonarcloud.io/dashboard?id=net.kemitix%3Amon)
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[](https://jenkins.kemitix.net/job/GitLab/job/kemitix%252Fmon/)
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[](https://jenkins.kemitix.net/job/GitLab/job/kemitix%252Fmon/)
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[](https://jenkins.kemitix.net/job/GitLab/job/kemitix%252Fmon/)
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[](https://app.codacy.com/project/kemitix/mon/dashboard)
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## Maven
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```xml
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<dependency>
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<groupId>net.kemitix</groupId>
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<artifactId>mon</artifactId>
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<version>0.6.0</version>
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</dependency>
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```
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## Usage
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### TypeAlias
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More of a type-wrapper really. It's as close as I could get to a Haskell type alias in Java.
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```java
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class Goal extends TypeAlias<String> {
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private Goal(final String goal) {
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super(goal);
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}
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public static Goal of(final String goal) {
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return new Goal(goal);
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}
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}
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```
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```java
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class Example {}
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Goal goal = Goal.of("goal");
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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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```
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### Maybe
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A non-final substitute for Optional with `peek()` and `stream()` methods.
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```java
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class Test {
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@Test
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public void maybeTests() {
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// Constructors: maybe(T), just(T) and nothing()
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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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// .orElseGet(Supplier<T>)
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assertThat(Maybe.nothing().orElseGet(() -> 1)).isEqualTo(1);
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assertThat(Maybe.just(1).orElseGet(() -> 2)).isEqualTo(1);
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// .orElse(Supplier<T>)
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assertThat(Maybe.nothing().orElse(1)).isEqualTo(1);
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assertThat(Maybe.just(1).orElse(2)).isEqualTo(1);
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// .filter(Predicate<T>)
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assertThat(Maybe.just(1).filter(v -> v > 2)).isEqualTo(Maybe.nothing());
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assertThat(Maybe.just(3).filter(v -> v > 2)).isEqualTo(Maybe.just(3));
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assertThat(Maybe.just(1).toOptional()).isEqualTo(Optional.of(1));
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assertThat(Maybe.nothing().toOptional()).isEqualTo(Optional.empty());
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// .fromOptional(Optional<T>) is deprecated
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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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// An alternative to using .fromOptional(Optional<T>)
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assertThat(Optional.of(1).map(Maybe::just).orElse(Maybe::nothing)).isEqualTo(Maybe.just(1));
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assertThat(Optional.empty().map(Maybe::just).orElse(Maybe::nothing)).isEqualTo(Maybe.nothing());
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// .peek(Consumer<T>)
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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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// .orElseThrow(Supplier<Exception>)
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assertThatCode(() -> Maybe.just(1).orElseThrow(IllegalStateException::new)).doesNotThrowAnyException();
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assertThatThrownBy(() -> Maybe.nothing().orElseThrow(IllegalStateException::new)).isInstanceOf(IllegalStateException.class);
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// .stream()
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assertThat(Maybe.just(1).stream()).containsExactly(1);
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assertThat(Maybe.nothing().stream()).isEmpty();
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}
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}
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```
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### Result
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A container for method return values that may raise an Exception. Useful for when a checked exceptions can't be added
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to the method signature.
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```java
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package net.kemitix.mon;
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import net.kemitix.mon.result.Result;
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import java.io.IOException;
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class ResultExample implements Runnable {
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public static void main(String[] args) {
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new ResultExample().run();
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}
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@Override
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public void run() {
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System.out.println("run");
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final Result<Integer> goodResult = goodMethod();
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if (goodResult.isOkay()) {
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doGoodThings();
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}
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if (goodResult.isError()) {
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notCalled(0);
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}
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goodResult.flatMap(number -> convertToString(number))
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.flatMap(str -> stringLength(str))
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.match(
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success -> System.out.format("Length is %s%n", success),
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error -> System.out.println("Count not determine length")
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);
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final Result<Integer> badResult = badMethod();
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badResult.match(
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success -> notCalled(success),
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error -> handleError(error)
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);
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}
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private Result<Integer> goodMethod() {
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System.out.println("goodMethod");
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return Result.ok(1);
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}
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private void doGoodThings() {
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System.out.println("doGoodThings");
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}
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private void notCalled(final Integer success) {
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System.out.println("notCalled");
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}
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private Result<String> convertToString(final Integer number) {
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System.out.println("convertToString");
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return Result.ok(String.valueOf(number));
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}
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private Result<Integer> stringLength(final String value) {
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System.out.println("stringLength");
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if (value == null) {
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return Result.error(new NullPointerException("value is null"));
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}
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return Result.ok(value.length());
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}
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// doesn't need to declare "throws IOException"
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private Result<Integer> badMethod() {
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System.out.println("badMethod");
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return Result.error(new IOException("error"));
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}
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private void handleError(final Throwable error) {
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System.out.println("handleError");
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throw new RuntimeException("Handled exception", error);
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}
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}
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```
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Will output:
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```text
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run
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goodMethod
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doGoodThings
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convertToString
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stringLength
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Length is 1
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badMethod
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handleError
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Exception in thread "main" java.lang.RuntimeException: Handled exception
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at net.kemitix.mon.ResultExample.handleError(ResultExample.java:72)
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at net.kemitix.mon.ResultExample.lambda$run$5(ResultExample.java:34)
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at net.kemitix.mon.result.Err.match(Err.java:56)
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at net.kemitix.mon.ResultExample.run(ResultExample.java:32)
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at net.kemitix.mon.ResultExample.main(ResultExample.java:10)
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Caused by: java.io.IOException: error
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at net.kemitix.mon.ResultExample.badMethod(ResultExample.java:67)
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at net.kemitix.mon.ResultExample.run(ResultExample.java:31)
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... 1 more
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```
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