Merge pull request #33 from kemitix/single-consumers-for-maybe-and-result

Single consumers for maybe and result

CHANGELOG

@@ -1,6 +1,13 @@
 CHANGELOG
 =========
 
+0.9.0
+-----
+
+* Add `Maybe.ifNothing(Runnable)`
+* Add `Result.recover(Function)`
+* Add `Result.onError(Consumer)`
+
 0.8.0
 -----
 

src/main/java/net/kemitix/mon/maybe/Just.java

@@ -93,6 +93,11 @@ final class Just<T> implements Maybe<T> {
         return this;
     }
 
+    @Override
+    public void ifNothing(final Runnable runnable) {
+        // ignore - not nothing
+    }
+
     @Override
     public void orElseThrow(final Supplier<Exception> e) {
         // do not throw

src/main/java/net/kemitix/mon/maybe/Maybe.java

@@ -142,4 +142,11 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
      * @return this Maybe
      */
     Maybe<T> peek(Consumer<T> consumer);
+
+    /**
+     * Run the runnable if the Maybe is a Nothing, otherwise do nothing.
+     *
+     * @param runnable the runnable to call if this is a Nothing
+     */
+    void ifNothing(Runnable runnable);
 }

src/main/java/net/kemitix/mon/maybe/Nothing.java

@@ -74,6 +74,11 @@ final class Nothing<T> implements Maybe<T> {
         return this;
     }
 
+    @Override
+    public void ifNothing(final Runnable runnable) {
+        runnable.run();
+    }
+
     @Override
     public void orElseThrow(final Supplier<Exception> e) throws Exception {
         throw e.get();

src/main/java/net/kemitix/mon/result/Err.java

@@ -80,6 +80,16 @@ class Err<T> implements Result<T> {
         return this;
     }
 
+    @Override
+    public Result<T> recover(final Function<Throwable, Result<T>> f) {
+        return f.apply(error);
+    }
+
+    @Override
+    public void onError(final Consumer<Throwable> errorConsumer) {
+        errorConsumer.accept(error);
+    }
+
     @Override
     public boolean equals(final Object other) {
         return other instanceof Err && Objects.equals(error, ((Err) other).error);

src/main/java/net/kemitix/mon/result/Result.java

@@ -94,7 +94,7 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * Creates a Result from the Maybe, where the Result will be an error if the Maybe is Nothing.
      *
      * @param result the Result the might contain the value of the Result
-     * @param <T>   the type of the Maybe and the Result
+     * @param <T>    the type of the Maybe and the Result
      * @return a Result containing the value of the Maybe when it is a Just, or the error when it is Nothing
      */
     @SuppressWarnings("illegalcatch")
@@ -108,8 +108,9 @@ public interface Result<T> extends Functor<T, Result<?>> {
 
     /**
      * Swaps the inner Result of a Maybe, so that a Result is on the outside.
+     *
      * @param maybeResult the Maybe the contains a Result
-     * @param <T> the type of the value that may be in the Result
+     * @param <T>         the type of the value that may be in the Result
      * @return a Result containing a Maybe, the value in the Maybe was the value in a successful Result within the
      * original Maybe. If the original Maybe is Nothing, the Result will contain Nothing. If the original Result was an
      * error, then the Result will also be an error.
@@ -177,4 +178,22 @@ public interface Result<T> extends Functor<T, Result<?>> {
      * @return this Result
      */
     Result<T> peek(Consumer<T> consumer);
+
+    /**
+     * Provide a way to attempt to recover from an error state.
+     *
+     * @param f the function to recover from the error
+     * @return a new Result, either a Success, or if recovery is not possible an other Err.
+     */
+    Result<T> recover(Function<Throwable, Result<T>> f);
+
+    /**
+     * A handler for error states.
+     *
+     * <p>When this is an error then tne Consumer will be supplier with the error. When this is a success, then nothing
+     * happens.</p>
+     *
+     * @param errorConsumer the consumer to handle the error
+     */
+    void onError(Consumer<Throwable> errorConsumer);
 }

src/main/java/net/kemitix/mon/result/Success.java

@@ -84,6 +84,16 @@ class Success<T> implements Result<T> {
         return this;
     }
 
+    @Override
+    public Result<T> recover(final Function<Throwable, Result<T>> f) {
+        return this;
+    }
+
+    @Override
+    public void onError(final Consumer<Throwable> errorConsumer) {
+        // do nothing - this is not an error
+    }
+
     @Override
     public boolean equals(final Object other) {
         return other instanceof Success && Objects.equals(value, ((Success) other).value);

src/test/java/net/kemitix/mon/MaybeTest.java

@@ -6,6 +6,7 @@ import org.junit.Test;
 
 import java.util.Objects;
 import java.util.Optional;
+import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.function.Predicate;
 import java.util.stream.Stream;
@@ -171,4 +172,26 @@ public class MaybeTest implements WithAssertions {
         assertThat(result.toOptional()).isEmpty();
     }
 
+    @Test
+    public void just_ifNothing_isIgnored() {
+        //given
+        final Maybe<Integer> just = Maybe.just(1);
+        final AtomicBoolean capture = new AtomicBoolean(false);
+        //when
+        just.ifNothing(() -> capture.set(true));
+        //then
+        assertThat(capture).isFalse();
+    }
+
+    @Test
+    public void nothing_ifNothing_isCalled() {
+        //given
+        final Maybe<Integer> nothing = Maybe.nothing();
+        final AtomicBoolean capture = new AtomicBoolean(false);
+        //when
+        nothing.ifNothing(() -> capture.set(true));
+        //then
+        assertThat(capture).isTrue();
+    }
+
 }

src/test/java/net/kemitix/mon/ResultTest.java

@@ -452,6 +452,54 @@ public class ResultTest implements WithAssertions {
         assertThat(peeked).isSameAs(result);
     }
 
+    @Test public void success_whenOnError_thenIgnore() {
+        //given
+        final Result<Integer> ok = Result.ok(1);
+        //when
+        ok.onError(e -> fail("not an error"));
+    }
+
+    @Test public void error_whenOnError_thenConsume() {
+        //given
+        final RuntimeException exception = new RuntimeException();
+        final Result<Integer> error = Result.error(exception);
+        final AtomicReference<Throwable> capture = new AtomicReference<>();
+        //when
+        error.onError(capture::set);
+        //then
+        assertThat(capture).hasValue(exception);
+    }
+
+    @Test
+    public void success_whenRecover_thenNoChange() {
+        //given
+        final Result<Integer> ok = Result.ok(1);
+        //when
+        final Result<Integer> recovered = ok.recover(e -> Result.ok(2));
+        //then
+        recovered.peek(v -> assertThat(v).isEqualTo(1));
+    }
+
+    @Test
+    public void error_whenRecover_thenSuccess() {
+        //given
+        final Result<Integer> error = Result.error(new RuntimeException());
+        //when
+        final Result<Integer> recovered = error.recover(e -> Result.ok(2));
+        //then
+        recovered.peek(v -> assertThat(v).isEqualTo(2));
+    }
+
+    @Test
+    public void error_whenRecoverFails_thenUpdatedError() {
+        //given
+        final Result<Integer> error = Result.error(new RuntimeException("original"));
+        //when
+        final Result<Integer> recovered = error.recover(e -> Result.error(new RuntimeException("updated")));
+        //then
+        recovered.onError(e -> assertThat(e).hasMessage("updated"));
+    }
+
     @RequiredArgsConstructor
     private static class UseCase {