From c5247d7c14e5e139f2595ff9165eb46e9669702a Mon Sep 17 00:00:00 2001
From: Paul Campbell <pcampbell@kemitix.net>
Date: Sat, 7 Jul 2018 18:21:35 +0100
Subject: [PATCH] Add `Maybe.ifNothing(Runnable)`

---
 CHANGELOG                                     |  5 ++++
 src/main/java/net/kemitix/mon/maybe/Just.java |  5 ++++
 .../java/net/kemitix/mon/maybe/Maybe.java     |  7 ++++++
 .../java/net/kemitix/mon/maybe/Nothing.java   |  5 ++++
 src/test/java/net/kemitix/mon/MaybeTest.java  | 23 +++++++++++++++++++
 5 files changed, 45 insertions(+)

diff --git a/CHANGELOG b/CHANGELOG
index e1f6ff8..c4444f2 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+0.9.0
+-----
+
+* Add `Maybe.ifNothing(Runnable)`
+
 0.8.0
 -----
 
diff --git a/src/main/java/net/kemitix/mon/maybe/Just.java b/src/main/java/net/kemitix/mon/maybe/Just.java
index 77a258f..85aea43 100644
--- a/src/main/java/net/kemitix/mon/maybe/Just.java
+++ b/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
diff --git a/src/main/java/net/kemitix/mon/maybe/Maybe.java b/src/main/java/net/kemitix/mon/maybe/Maybe.java
index 02b1ffc..be04b67 100644
--- a/src/main/java/net/kemitix/mon/maybe/Maybe.java
+++ b/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);
 }
diff --git a/src/main/java/net/kemitix/mon/maybe/Nothing.java b/src/main/java/net/kemitix/mon/maybe/Nothing.java
index 05f033d..d1c7193 100644
--- a/src/main/java/net/kemitix/mon/maybe/Nothing.java
+++ b/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();
diff --git a/src/test/java/net/kemitix/mon/MaybeTest.java b/src/test/java/net/kemitix/mon/MaybeTest.java
index 575826a..2b82337 100644
--- a/src/test/java/net/kemitix/mon/MaybeTest.java
+++ b/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();
+    }
+
 }