private function loadSource($source, Mustache_Cache $cache = null)
    {
        $className = $this->getTemplateClassName($source);

        if (!isset($this->templates[$className])) {
            if ($cache === null) {
                $cache = $this->getCache();
            }

            if (!class_exists($className, false)) {
                if (!$cache->load($className)) {
                    $compiled = $this->compile($source);
                    $cache->cache($className, $compiled);
                }
            }

            $this->log(
                Mustache_Logger::DEBUG,
                'Instantiating template: "{className}"',
                array('className' => $className)
            );

            $this->templates[$className] = new $className($this);
        }

        return $this->templates[$className];
    }