Add thenWith(Function)

CHANGELOG

@@ -5,6 +5,7 @@ CHANGELOG
 ------
 
 * Add `andThen(Function)`
+* Add `thenWith(Function)`
 
 0.9.0
 -----

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

@@ -96,6 +96,11 @@ class Err<T> implements Result<T> {
         return Result.error(error);
     }
 
+    @Override
+    public Result<T> thenWith(final Function<T, WithResultContinuation<T>> f) {
+        return this;
+    }
+
     @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

@@ -202,7 +202,6 @@ public interface Result<T> extends Functor<T, Result<?>> {
      *
      * <p>Combination of {@link #flatMap(Function)} and {@link #of(Callable)}.</p>
      *
-     * <p>Syntax is:</p>
      * <pre><code>
      *     Integer doSomething() {...}
      *     String doSomethingElse(final Integer value) {...}
@@ -212,9 +211,29 @@ public interface Result<T> extends Functor<T, Result<?>> {
      *
      * <p>When the Result is an Err, then the original error is carried over and the Callable is never called.</p>
      *
-     * @param f   the function to map the Success value to the Callable
+     * @param f   the function to map the Success value into the Callable
      * @param <R> the type of the final Result
      * @return a new Result
      */
     <R> Result<R> andThen(Function<T, Callable<R>> f);
+
+    /**
+     * Perform the continuation with the current Result value then return the current Result, assuming there was no
+     * error in the continuation.
+     *
+     * <pre><code>
+     *     Integer doSomething() {...}
+     *     void doSomethingElse(final Integer value) {...}
+     *     Result&lt;Integer&gt; r = Result.of(() -&gt; doSomething())
+     *                              .thenWith(value -&gt; () -&gt; doSomethingElse(value));
+     * </code></pre>
+     *
+     * <p>Where the Result is an Err, then the Result is returned immediately and the continuation is ignored.</p>
+     * <p>Where the Result is a Success, then if an exception is thrown by the continuation the Result returned will be
+     * a new error Result containing that exception, otherwise the original Result will be returned.</p>
+     *
+     * @param f the function to map the Success value into the result continuation
+     * @return the Result or a new error Result
+     */
+    Result<T> thenWith(Function<T, WithResultContinuation<T>> f);
 }

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

@@ -100,6 +100,11 @@ class Success<T> implements Result<T> {
         return Result.of(f.apply(value));
     }
 
+    @Override
+    public Result<T> thenWith(final Function<T, WithResultContinuation<T>> f) {
+        return f.apply(value).call(this);
+    }
+
     @Override
     public boolean equals(final Object other) {
         return other instanceof Success && Objects.equals(value, ((Success) other).value);

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

@@ -0,0 +1,49 @@
+/**
+ * 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.result;
+
+/**
+ * A Callable-like interface for performing an action with a Result that, if there are no errors is returned as-is, but
+ * if there is an error then a new error Result is returned.
+ *
+ * @param <T> the type of the current Result value
+ */
+@FunctionalInterface
+public interface WithResultContinuation<T> {
+
+    /**
+     * Method to make use of the Result value.
+     *
+     * @throws Exception to replace the current Result with an error
+     */
+    void run() throws Exception;
+
+    @SuppressWarnings({"illegalcatch", "javadocmethod"})
+    default Result<T> call(final Result<T> currentResult) {
+        try {
+            run();
+        } catch (Throwable e) {
+            return Result.error(e);
+        }
+        return currentResult;
+    }
+}

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

@@ -540,7 +540,7 @@ public class ResultTest implements WithAssertions {
     }
 
     @Test
-    public void error_andThenError_thenError() {
+    public void error_andThenError_thenOriginalError() {
         //given
         final RuntimeException exception1 = new RuntimeException();
         final Result<Object> error = Result.error(exception1);
@@ -553,6 +553,61 @@ public class ResultTest implements WithAssertions {
         result.onError(e -> assertThat(e).isSameAs(exception1));
     }
 
+    @Test
+    public void success_whenThenWith_whenOkay_thenSuccess() {
+        //given
+        final Result<Integer> ok = Result.ok(1);
+        //when
+        final Result<Integer> result = ok.thenWith(v -> () -> {
+            // do something with v
+        });
+        //then
+        assertThat(result.isOkay()).isTrue();
+        result.peek(v -> assertThat(v).isEqualTo(1));
+    }
+
+    @Test
+    public void success_whenThenWith_whenError_thenError() {
+        //given
+        final Result<Integer> ok = Result.ok(1);
+        final RuntimeException exception = new RuntimeException();
+        //when
+        final Result<Integer> result = ok.thenWith(v -> () -> {
+            throw exception;
+        });
+        //then
+        assertThat(result.isError()).isTrue();
+        result.onError(e -> assertThat(e).isSameAs(exception));
+    }
+
+    @Test
+    public void error_whenThenWith_whenOkay_thenError() {
+        //given
+        final RuntimeException exception = new RuntimeException();
+        final Result<Integer> error = Result.error(exception);
+        //when
+        final Result<Integer> result = error.thenWith(v -> () -> {
+            // do something with v
+        });
+        //then
+        assertThat(result.isError()).isTrue();
+        result.onError(e -> assertThat(e).isSameAs(exception));
+    }
+
+    @Test
+    public void error_whenThenWith_whenError_thenOriginalError() {
+        //given
+        final RuntimeException exception = new RuntimeException();
+        final Result<Integer> error = Result.error(exception);
+        //when
+        final Result<Integer> result = error.thenWith(v -> () -> {
+            throw new RuntimeException();
+        });
+        //then
+        assertThat(result.isError()).isTrue();
+        result.onError(e -> assertThat(e).isSameAs(exception));
+    }
+
     @RequiredArgsConstructor
     private static class UseCase {