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/Command/Processor/ProcessorChain.php

@@ -0,0 +1,130 @@
+<?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\Command\Processor;
+
+use Predis\Command\CommandInterface;
+
+/**
+ * Default implementation of a command processors chain.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+class ProcessorChain implements CommandProcessorChainInterface, \ArrayAccess
+{
+    private $processors = array();
+
+    /**
+     * @param array $processors List of instances of CommandProcessorInterface.
+     */
+    public function __construct($processors = array())
+    {
+        foreach ($processors as $processor) {
+            $this->add($processor);
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function add(CommandProcessorInterface $processor)
+    {
+        $this->processors[] = $processor;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function remove(CommandProcessorInterface $processor)
+    {
+        if (false !== $index = array_search($processor, $this->processors, true)) {
+            unset($this[$index]);
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function process(CommandInterface $command)
+    {
+        for ($i = 0; $i < $count = count($this->processors); $i++) {
+            $this->processors[$i]->process($command);
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getProcessors()
+    {
+        return $this->processors;
+    }
+
+    /**
+     * Returns an iterator over the list of command processor in the chain.
+     *
+     * @return \ArrayIterator
+     */
+    public function getIterator()
+    {
+        return new \ArrayIterator($this->processors);
+    }
+
+    /**
+     * Returns the number of command processors in the chain.
+     *
+     * @return int
+     */
+    public function count()
+    {
+        return count($this->processors);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function offsetExists($index)
+    {
+        return isset($this->processors[$index]);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function offsetGet($index)
+    {
+        return $this->processors[$index];
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function offsetSet($index, $processor)
+    {
+        if (!$processor instanceof CommandProcessorInterface) {
+            throw new \InvalidArgumentException(
+                'A processor chain can hold only instances of classes implementing '.
+                'the Predis\Command\Processor\CommandProcessorInterface interface'
+            );
+        }
+
+        $this->processors[$index] = $processor;
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function offsetUnset($index)
+    {
+        unset($this->processors[$index]);
+        $this->processors = array_values($this->processors);
+    }
+}