Retwis ported to modern Redis data types.

The example (and related documentation at redis.io) was not updated for
5 years. Redis had no sorted sets and hashes when the original code was
written (!). An update was really needed.

We also use a modern PHP client now: Predis. A copy is shipped within
this repository to make life easier to newcomers trying Redis for the
first time via this example.

Predis/Iterator/MultiBulkResponseTuple.php

@@ -0,0 +1,83 @@
+<?php
+
+/*
+ * This file is part of the Predis package.
+ *
+ * (c) Daniele Alessandri <suppakilla@gmail.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Predis\Iterator;
+
+/**
+ * Abstracts the access to a streamable list of tuples represented
+ * as a multibulk reply that alternates keys and values.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+class MultiBulkResponseTuple extends MultiBulkResponse implements \OuterIterator
+{
+    private $iterator;
+
+    /**
+     * @param MultiBulkResponseSimple $iterator Multibulk reply iterator.
+     */
+    public function __construct(MultiBulkResponseSimple $iterator)
+    {
+        $this->checkPreconditions($iterator);
+
+        $virtualSize = count($iterator) / 2;
+        $this->iterator = $iterator;
+        $this->position = $iterator->getPosition();
+        $this->current = $virtualSize > 0 ? $this->getValue() : null;
+        $this->replySize = $virtualSize;
+    }
+
+    /**
+     * Checks for valid preconditions.
+     *
+     * @param MultiBulkResponseSimple $iterator Multibulk reply iterator.
+     */
+    protected function checkPreconditions(MultiBulkResponseSimple $iterator)
+    {
+        if ($iterator->getPosition() !== 0) {
+            throw new \RuntimeException('Cannot initialize a tuple iterator with an already initiated iterator');
+        }
+
+        if (($size = count($iterator)) % 2 !== 0) {
+            throw new \UnexpectedValueException("Invalid reply size for a tuple iterator [$size]");
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getInnerIterator()
+    {
+        return $this->iterator;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function __destruct()
+    {
+        $this->iterator->sync(true);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function getValue()
+    {
+        $k = $this->iterator->current();
+        $this->iterator->next();
+
+        $v = $this->iterator->current();
+        $this->iterator->next();
+
+        return array($k, $v);
+    }
+}