From 9923bbc880d75dd762e14f2f5b8fc6b37fecd775 Mon Sep 17 00:00:00 2001
From: Paul Campbell <pcampbell@kemitix.net>
Date: Sat, 30 Jun 2018 18:13:29 +0100
Subject: [PATCH] Add `Result.peek(Consumer)`

---
 .../java/net/kemitix/mon/maybe/Maybe.java     |  4 +--
 src/main/java/net/kemitix/mon/result/Err.java |  6 +++++
 .../java/net/kemitix/mon/result/Result.java   |  8 ++++++
 .../java/net/kemitix/mon/result/Success.java  |  7 ++++++
 src/test/java/net/kemitix/mon/ResultTest.java | 25 +++++++++++++++++++
 5 files changed, 48 insertions(+), 2 deletions(-)

diff --git a/src/main/java/net/kemitix/mon/maybe/Maybe.java b/src/main/java/net/kemitix/mon/maybe/Maybe.java
index b4fffd8..02b1ffc 100644
--- a/src/main/java/net/kemitix/mon/maybe/Maybe.java
+++ b/src/main/java/net/kemitix/mon/maybe/Maybe.java
@@ -136,10 +136,10 @@ public interface Maybe<T> extends Functor<T, Maybe<?>> {
     Maybe<T> filter(Predicate<T> predicate);
 
     /**
-     * Provide the value within the Maybe, if it exists, to the Supplier, and returns the Maybe.
+     * Provide the value within the Maybe, if it exists, to the Consumer, and returns this Maybe.
      *
      * @param consumer the Consumer to the value if present
-     * @return the Maybe
+     * @return this Maybe
      */
     Maybe<T> peek(Consumer<T> consumer);
 }
diff --git a/src/main/java/net/kemitix/mon/result/Err.java b/src/main/java/net/kemitix/mon/result/Err.java
index e197dea..0e54336 100644
--- a/src/main/java/net/kemitix/mon/result/Err.java
+++ b/src/main/java/net/kemitix/mon/result/Err.java
@@ -35,6 +35,7 @@ import java.util.function.Predicate;
  * @param <T> the type of the value in the Result if it has been a success
  */
 @RequiredArgsConstructor
+@SuppressWarnings("methodcount")
 class Err<T> implements Result<T> {
 
     private final Throwable error;
@@ -74,6 +75,11 @@ class Err<T> implements Result<T> {
         throw error;
     }
 
+    @Override
+    public Result<T> peek(final Consumer<T> consumer) {
+        return this;
+    }
+
     @Override
     public boolean equals(final Object other) {
         return other instanceof Err && Objects.equals(error, ((Err) other).error);
diff --git a/src/main/java/net/kemitix/mon/result/Result.java b/src/main/java/net/kemitix/mon/result/Result.java
index 30043e2..4dd6d65 100644
--- a/src/main/java/net/kemitix/mon/result/Result.java
+++ b/src/main/java/net/kemitix/mon/result/Result.java
@@ -169,4 +169,12 @@ public interface Result<T> extends Functor<T, Result<?>> {
      */
     @SuppressWarnings("illegalthrows")
     T orElseThrow() throws Throwable;
+
+    /**
+     * Provide the value within the Result, if it is a success, to the Consumer, and returns this Result.
+     *
+     * @param consumer the Consumer to the value if a success
+     * @return this Result
+     */
+    Result<T> peek(Consumer<T> consumer);
 }
diff --git a/src/main/java/net/kemitix/mon/result/Success.java b/src/main/java/net/kemitix/mon/result/Success.java
index ec2aa58..7c880fa 100644
--- a/src/main/java/net/kemitix/mon/result/Success.java
+++ b/src/main/java/net/kemitix/mon/result/Success.java
@@ -35,6 +35,7 @@ import java.util.function.Predicate;
  * @param <T> the type of the value in the Result
  */
 @RequiredArgsConstructor
+@SuppressWarnings("methodcount")
 class Success<T> implements Result<T> {
 
     private final T value;
@@ -77,6 +78,12 @@ class Success<T> implements Result<T> {
         return value;
     }
 
+    @Override
+    public Result<T> peek(final Consumer<T> consumer) {
+        consumer.accept(value);
+        return this;
+    }
+
     @Override
     public boolean equals(final Object other) {
         return other instanceof Success && Objects.equals(value, ((Success) other).value);
diff --git a/src/test/java/net/kemitix/mon/ResultTest.java b/src/test/java/net/kemitix/mon/ResultTest.java
index e8b24cd..9e5c52c 100644
--- a/src/test/java/net/kemitix/mon/ResultTest.java
+++ b/src/test/java/net/kemitix/mon/ResultTest.java
@@ -8,6 +8,7 @@ import org.junit.Test;
 
 import java.io.IOException;
 import java.util.concurrent.Callable;
+import java.util.concurrent.atomic.AtomicReference;
 
 public class ResultTest implements WithAssertions {
 
@@ -427,6 +428,30 @@ public class ResultTest implements WithAssertions {
         );
     }
 
+    @Test
+    public void success_peek_consumes() {
+        //given
+        final Result<Integer> result = Result.ok(1);
+        final AtomicReference<Integer> consumed = new AtomicReference<>(0);
+        //when
+        final Result<Integer> peeked = result.peek(consumed::set);
+        //then
+        assertThat(consumed).hasValue(1);
+        assertThat(peeked).isSameAs(result);
+    }
+
+    @Test
+    public void error_peek_doesNothing() {
+        //given
+        final Result<Integer> result = Result.error(new RuntimeException());
+        final AtomicReference<Integer> consumed = new AtomicReference<>(0);
+        //when
+        final Result<Integer> peeked = result.peek(consumed::set);
+        //then
+        assertThat(consumed).hasValue(0);
+        assertThat(peeked).isSameAs(result);
+    }
+
     @RequiredArgsConstructor
     private static class UseCase {