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/Pipeline/FireAndForgetExecutor.php

@@ -0,0 +1,55 @@
+<?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\Pipeline;
+
+use SplQueue;
+use Predis\Connection\ConnectionInterface;
+use Predis\Connection\ReplicationConnectionInterface;
+
+/**
+ * Implements a pipeline executor strategy that writes a list of commands to
+ * the connection object but does not read back their replies.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+class FireAndForgetExecutor implements PipelineExecutorInterface
+{
+    /**
+     * Allows the pipeline executor to perform operations on the
+     * connection before starting to execute the commands stored
+     * in the pipeline.
+     *
+     * @param ConnectionInterface $connection Connection instance.
+     */
+    protected function checkConnection(ConnectionInterface $connection)
+    {
+        if ($connection instanceof ReplicationConnectionInterface) {
+            $connection->switchTo('master');
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function execute(ConnectionInterface $connection, SplQueue $commands)
+    {
+        $this->checkConnection($connection);
+
+        while (!$commands->isEmpty()) {
+            $connection->writeCommand($commands->dequeue());
+        }
+
+        $connection->disconnect();
+
+        return array();
+    }
+}