Merge pull request #174 from Kevin-Lee/task/168/add-Either.getLeftOrElse

Close #168 - Add Either.getLeftOrElse

src/main/java/j8plus/types/Either.java

@@ -36,6 +36,8 @@ public abstract <C> C fold(
 
   public abstract B getOrElse(Supplier<B> alternative);
 
+  public abstract A getLeftOrElse(Supplier<A> alternative);
+
   public abstract void forEach(Consumer<? super B> f);
 
   public abstract Optional<B> toOptional();
@@ -140,6 +142,11 @@ public B getOrElse(final Supplier<B> alternative) {
       return alternative.get();
     }
 
+    @Override
+    public A getLeftOrElse(final Supplier<A> alternative) {
+      return this.value;
+    }
+
     @Override
     public void forEach(final Consumer<? super B> f) {
     }
@@ -232,6 +239,11 @@ public B getOrElse(final Supplier<B> alternative) {
       return this.value;
     }
 
+    @Override
+    public A getLeftOrElse(final Supplier<A> alternative) {
+      return alternative.get();
+    }
+
     @Override
     public void forEach(final Consumer<? super B> f) {
       f.accept(this.value);

src/test/java/j8plus/types/EitherTest.java

@@ -361,6 +361,38 @@ public void getOrElse_RightCase() {
       );
   }
 
+  @Test
+  public void getLeftOrElse_LeftCase() {
+    final String input = "Some error";
+    final String expected = input;
+    test("Either.getLeftOrElse on Left", "Either.getLeftOrElse on Left should return the the Left value")
+      .when(() ->
+        Either.<String, Integer>left(input)
+      )
+      .then(actual ->
+        assertThat(actual.isLeft()).isTrue()
+      )
+      .then(actual ->
+        assertThat(actual.getLeftOrElse(() -> expected)).isEqualTo(expected)
+      );
+  }
+
+  @Test
+  public void getLeftOrElse_RightCase() {
+    final Integer input = 999;
+    final String expected = "Alternative message";
+    test("Either.getLeftOrElse on Right", "Either.getLeftOrElse on Right should return the given alternative")
+      .when(() ->
+        Either.<String, Integer>right(input)
+      )
+      .then(actual ->
+        assertThat(actual.isRight()).isTrue()
+      )
+      .then(actual ->
+        assertThat(actual.getLeftOrElse(() -> expected)).isEqualTo(expected)
+      );
+  }
+
   @Test
   public void forEach_LeftCase() {
     final String input = "Some error";