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