gistfile1.txt

interface ConfigFileInterface 
{
    public function load();
    public function save();    
}

class YamlConfigFile implements ConfigFileInterface
{
    public function load()
    {
    
    }
    
    public function save()
    {
    
    }
}   

class ConfigFile implements \ArrayAccess
{
    /**
     * @var ConfigFileInterface
     */
    protected $config;

    /**
     * @param ConfigFileInterface
     */
    public function __construct(ConfigFileInterface $config)
    {
        $this->config = $config;
    }
}

$config = new ConfigFile(
    YamlConfigFile('config.yml')
);

echo $config['timeout']; // 10
echo $config['parameter']['a']; // 1;
echo $config->get('name'); // abc