php convert index array to json

public static function encode(&$var)
{
 return '{'.implode(',',self::encodeExcute($var)).'}';
}
private static function encodeExcute(&$var)
{
 $json = array();
 switch (gettype($var))
 {
  case 'array':
   foreach($var as $key=>$value)
   {
    if(is_array($value))
    {
     $json[] = '"'.$key.'":{'.implode(',',self::encodeExcute($value)).'}';
     //$json[$key] = self::encode($value);
    } elseif (is_object($value)) {
     $json[] = "\\"{$key}\\":".json_encode($value->attributes);
    } else {
     echo 'ERROR 未知类型,还未解析';
     Yii::app()->end();
    }
   }
   break;
  case 'object':
   break;
 }
 return $json;
}