Handle incocmpatible versions for dev/perf deployments

2 files changed, 74 insertions, 0 deletions

diff --git a/vespajlib/src/main/java/com/yahoo/collections/Iterables.java b/vespajlib/src/main/java/com/yahoo/collections/Iterables.java
new file mode 100644
index 00000000000..904db7a3db7
--- /dev/null
+++ b/vespajlib/src/main/java/com/yahoo/collections/Iterables.java
@@ -0,0 +1,25 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.collections;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+
+/**
+ * @author jonmv
+ */
+public class Iterables {
+
+    private Iterables() { }
+
+    /** Returns a reverse-order iterable view of the given elements. */
+    public static <T> Iterable<T> reversed(List<T> elements) {
+        return () -> new Iterator<T>() {
+            final ListIterator<T> wrapped = elements.listIterator(elements.size());
+            @Override public boolean hasNext() { return wrapped.hasPrevious(); }
+            @Override public T next() { return wrapped.previous(); }
+            @Override public void remove() { wrapped.remove(); }
+        };
+    }
+
+}
diff --git a/vespajlib/src/test/java/com/yahoo/collections/IterablesTest.java b/vespajlib/src/test/java/com/yahoo/collections/IterablesTest.java
new file mode 100644
index 00000000000..40be8831f0b
--- /dev/null
+++ b/vespajlib/src/test/java/com/yahoo/collections/IterablesTest.java
@@ -0,0 +1,49 @@
+// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.collections;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * @author jonmv
+ */
+class IterablesTest {
+
+    @Test
+    void testEmpty() {
+        List<Integer> elements = new ArrayList<>();
+        Iterator<Integer> iterator = Iterables.reversed(elements).iterator();
+        assertFalse(iterator.hasNext());
+        assertThrows(NoSuchElementException.class, iterator::next);
+        assertThrows(IllegalStateException.class, iterator::remove);
+    }
+
+    @Test
+    void testIterator() {
+        List<Integer> elements = new ArrayList<>(List.of(1, 2, 3));
+        Iterator<Integer> iterator = Iterables.reversed(elements).iterator();
+        assertTrue(iterator.hasNext());
+        assertEquals(3, iterator.next());
+        iterator.remove();
+        assertThrows(IllegalStateException.class, iterator::remove);
+        assertTrue(iterator.hasNext());
+        assertEquals(2, iterator.next());
+        assertTrue(iterator.hasNext());
+        assertEquals(1, iterator.next());
+        iterator.remove();
+        assertThrows(IllegalStateException.class, iterator::remove);
+        assertThrows(NoSuchElementException.class, iterator::next);
+        assertEquals(List.of(2), elements);
+    }
+
+}