Intersperse

jnape · jnape · commit 745d308f74d8 · 2017-01-29T15:01:51.000-06:00
diff --git a/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn2/Intersperse.java b/src/main/java/com/jnape/palatable/lambda/functions/builtin/fn2/Intersperse.java
@@ -0,0 +1,33 @@
+package com.jnape.palatable.lambda.functions.builtin.fn2;
+
+import com.jnape.palatable.lambda.functions.Fn1;
+import com.jnape.palatable.lambda.functions.Fn2;
+
+import static com.jnape.palatable.lambda.functions.builtin.fn1.Tail.tail;
+import static com.jnape.palatable.lambda.functions.builtin.fn2.PrependAll.prependAll;
+
+public final class Intersperse<A> implements Fn2<A, Iterable<A>, Iterable<A>> {
+
+    private static final Intersperse INSTANCE = new Intersperse();
+
+    private Intersperse() {
+    }
+
+    @Override
+    public Iterable<A> apply(A a, Iterable<A> as) {
+        return tail(prependAll(a, as));
+    }
+
+    @SuppressWarnings("unchecked")
+    public static <A> Intersperse<A> intersperse() {
+        return INSTANCE;
+    }
+
+    public static <A> Fn1<Iterable<A>, Iterable<A>> intersperse(A a) {
+        return Intersperse.<A>intersperse().apply(a);
+    }
+
+    public static <A> Iterable<A> intersperse(A a, Iterable<A> as) {
+        return intersperse(a).apply(as);
+    }
+}
diff --git a/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn2/IntersperseTest.java b/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn2/IntersperseTest.java
@@ -0,0 +1,37 @@
+package com.jnape.palatable.lambda.functions.builtin.fn2;
+
+import com.jnape.palatable.lambda.functions.Fn1;
+import com.jnape.palatable.traitor.annotations.TestTraits;
+import com.jnape.palatable.traitor.runners.Traits;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import testsupport.traits.FiniteIteration;
+import testsupport.traits.ImmutableIteration;
+import testsupport.traits.InfiniteIterableSupport;
+import testsupport.traits.Laziness;
+
+import static com.jnape.palatable.lambda.functions.builtin.fn2.Intersperse.intersperse;
+import static java.util.Arrays.asList;
+import static java.util.Collections.emptyList;
+import static org.junit.Assert.assertThat;
+import static testsupport.matchers.IterableMatcher.isEmpty;
+import static testsupport.matchers.IterableMatcher.iterates;
+
+@RunWith(Traits.class)
+public class IntersperseTest {
+
+    @TestTraits({Laziness.class, FiniteIteration.class, ImmutableIteration.class, InfiniteIterableSupport.class})
+    public Fn1<Iterable<Object>, Iterable<Object>> testSubject() {
+        return intersperse(0);
+    }
+
+    @Test
+    public void interspersesBetweenElementsInIterable() {
+        assertThat(intersperse(0, asList(1, 2, 3)), iterates(1, 0, 2, 0, 3));
+    }
+
+    @Test
+    public void doesNotIntersperseEmptyIterable() {
+        assertThat(intersperse(0, emptyList()), isEmpty());
+    }
+}
diff --git a/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn2/PrependAllTest.java b/src/test/java/com/jnape/palatable/lambda/functions/builtin/fn2/PrependAllTest.java
@@ -8,6 +8,7 @@
 import testsupport.traits.EmptyIterableSupport;
 import testsupport.traits.FiniteIteration;
 import testsupport.traits.ImmutableIteration;
+import testsupport.traits.InfiniteIterableSupport;
 import testsupport.traits.Laziness;
 
 import static com.jnape.palatable.lambda.functions.builtin.fn2.PrependAll.prependAll;
@@ -20,7 +21,7 @@
 @RunWith(Traits.class)
 public class PrependAllTest {
 
-    @TestTraits({Laziness.class, FiniteIteration.class, EmptyIterableSupport.class, ImmutableIteration.class})
+    @TestTraits({Laziness.class, FiniteIteration.class, EmptyIterableSupport.class, ImmutableIteration.class, InfiniteIterableSupport.class})
     public Fn1<Iterable<Object>, Iterable<Object>> testSubject() {
         return prependAll(0);
     }
diff --git a/src/test/java/testsupport/traits/InfiniteIterableSupport.java b/src/test/java/testsupport/traits/InfiniteIterableSupport.java
@@ -0,0 +1,28 @@
+package testsupport.traits;
+
+import com.jnape.palatable.lambda.functions.Fn1;
+import com.jnape.palatable.traitor.traits.Trait;
+
+import java.util.concurrent.CountDownLatch;
+
+import static com.jnape.palatable.lambda.functions.builtin.fn1.Repeat.repeat;
+import static java.util.concurrent.TimeUnit.SECONDS;
+import static org.junit.Assert.fail;
+
+public class InfiniteIterableSupport implements Trait<Fn1<Iterable, Iterable>> {
+
+    @Override
+    public void test(Fn1<Iterable, Iterable> testSubject) {
+        CountDownLatch latch = new CountDownLatch(1);
+        new Thread(() -> {
+            testSubject.apply(repeat(0)).iterator().next();
+            latch.countDown();
+        }).start();
+        try {
+            if (!latch.await(1, SECONDS))
+                fail("Termination when given an infinite iterable could not be proven in time");
+        } catch (InterruptedException e) {
+            throw new AssertionError("interrupted", e);
+        }
+    }
+}
