doufo.ConverterDict().register(): A decorator factory to define typing converting decorator
            Attributes:  
                `self`
                `src` (`type`): source `type`,
                `tar` (`type`): target `type`,
            Returns:
                `f` (`Callable[[T], B]`): a decorater that defines a converter

def register(self, src: type, tar: type) -> Callable[[T], B]:
        """doufo.ConverterDict().register(): A decorator factory to define typing converting decorator
            Attributes:  
                `self`
                `src` (`type`): source `type`,
                `tar` (`type`): target `type`,
            Returns:
                `f` (`Callable[[T], B]`): a decorater that defines a converter                
        """
        def deco(f):
            self.converters[(src, tar)] = f
            self.converters = self.sorted_converters_keys()
            return f
        return deco