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/Option/CustomOption.php

@@ -0,0 +1,89 @@
+<?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\Option;
+
+/**
+ * Implements a generic class used to dynamically define a client option.
+ *
+ * @author Daniele Alessandri <suppakilla@gmail.com>
+ */
+class CustomOption implements OptionInterface
+{
+    private $filter;
+    private $default;
+
+    /**
+     * @param array $options List of options
+     */
+    public function __construct(Array $options = array())
+    {
+        $this->filter = $this->ensureCallable($options, 'filter');
+        $this->default = $this->ensureCallable($options, 'default');
+    }
+
+    /**
+     * Checks if the specified value in the options array is a callable object.
+     *
+     * @param array  $options Array of options
+     * @param string $key     Target option.
+     */
+    private function ensureCallable($options, $key)
+    {
+        if (!isset($options[$key])) {
+            return;
+        }
+
+        if (is_callable($callable = $options[$key])) {
+            return $callable;
+        }
+
+        throw new \InvalidArgumentException("The parameter $key must be callable");
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function filter(ClientOptionsInterface $options, $value)
+    {
+        if (isset($value)) {
+            if ($this->filter === null) {
+                return $value;
+            }
+
+            return call_user_func($this->filter, $options, $value);
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function getDefault(ClientOptionsInterface $options)
+    {
+        if (!isset($this->default)) {
+            return;
+        }
+
+        return call_user_func($this->default, $options);
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function __invoke(ClientOptionsInterface $options, $value)
+    {
+        if (isset($value)) {
+            return $this->filter($options, $value);
+        }
+
+        return $this->getDefault($options);
+    }
+}