original_string: public static function get_driver_instance($type, $library, $external = false) {
          global $CFG;
  
          $classname = $type.'_'.$library.'_moodle_database';
          $libfile   = "$CFG->libdir/dml/$classname.php";
  
          if (!file_exists($libfile)) {
              return null;
          }
  
          require_once($libfile);
          return new $classname($external);
      }
code: public static function get_driver_instance($type, $library, $external = false) {
          global $CFG;
  
          $classname = $type.'_'.$library.'_moodle_database';
          $libfile   = "$CFG->libdir/dml/$classname.php";
  
          if (!file_exists($libfile)) {
              return null;
          }
  
          require_once($libfile);
          return new $classname($external);
      }
code_tokens: public static function get_driver_instance ( $ type , $ library , $ external = false ) { global $ CFG ; $ classname = $ type . '_' . $ library . '_moodle_database' ; $ libfile = "$CFG->libdir/dml/$classname.php" ; if ( ! file_exists ( $ libfile ) ) { return null ; } require_once ( $ libfile ) ; return new $ classname ( $ external ) ; }
docstring: Loads and returns a database instance with the specified type and library.
  
  The loaded class is within lib/dml directory and of the form: $type.'_'.$library.'_moodle_database'
  
  @param string $type Database driver's type. (eg: mysqli, pgsql, mssql, sqldrv, oci, etc.)
  @param string $library Database driver's library (native, pdo, etc.)
  @param bool $external True if this is an external database.
  @return moodle_database driver object or null if error, for example of driver object see {@link mysqli_native_moodle_database}
docstring_tokens: Loads and returns a database instance with the specified type and library .