A helper method that makes passing custom validators implemented as
        methods to :class:`incoming.datatypes.Function` instances.

def _replace_string_args(self):
        '''
        A helper method that makes passing custom validators implemented as
        methods to :class:`incoming.datatypes.Function` instances.
        '''

        if self._string_args_replaced:
            return

        for field in self._fields:
            field = getattr(self, field)
            if isinstance(field, Function):
                if isinstance(field.func, str):
                    field.func = getattr(self, field.func)
            elif isinstance(field, JSON):
                if isinstance(field.cls, str):
                    field.cls = getattr(self, field.cls)

        self._string_args_replaced = True