adding last to retrieve the last element of an iterable

jnape · jnape · commit 00a4a37ca90a · 2017-01-08T13:51:37.000-06:00
diff --git a/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn1/Last.java b/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn1/Last.java
@@ -0,0 +1,37 @@
+package com.jnape.palatable.lambda.functions.builtin.fn1;
+
+import com.jnape.palatable.lambda.functions.Fn1;
+
+import java.util.Optional;
+
+/**
+ * Retrieve the last element of an <code>Iterable</code>, wrapped in an <code>Optional</code>. If the
+ * <code>Iterable</code> is empty, the result is <code>Optional.empty()</code>.
+ *
+ * @param <A> the Iterable element type
+ */
+public final class Last<A> implements Fn1<Iterable<A>, Optional<A>> {
+
+    private static final Last INSTANCE = new Last();
+
+    private Last() {
+    }
+
+    @Override
+    public Optional<A> apply(Iterable<A> as) {
+        A last = null;
+        for (A a : as) {
+            last = a;
+        }
+        return Optional.ofNullable(last);
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <A> Last<A> last() {
+        return (Last<A>) INSTANCE;
+    }
+
+    public static <A> Optional<A> last(Iterable<A> as) {
+        return Last.<A>last().apply(as);
+    }
+}
diff --git a/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn1/LastTest.java b/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn1/LastTest.java
@@ -0,0 +1,23 @@
+package com.jnape.palatable.lambda.functions.builtin.fn1;
+
+import org.junit.Test;
+
+import java.util.Optional;
+
+import static com.jnape.palatable.lambda.functions.builtin.fn1.Last.last;
+import static java.util.Arrays.asList;
+import static java.util.Collections.emptyList;
+import static org.junit.Assert.assertEquals;
+
+public class LastTest {
+
+    @Test
+    public void presentForNonEmptyIterable() {
+        assertEquals(Optional.of(3), last(asList(1, 2, 3)));
+    }
+
+    @Test
+    public void emptyForEmpyIterables() {
+        assertEquals(Optional.empty(), last(emptyList()));
+    }
+}
