How to use the stone.backends.obj_c_helpers.fmt_var function in stone

def _generate_route_signature(
            self,
            route,
            namespace,  # pylint: disable=unused-argument
            route_args,
            extra_args,
            doc_list,
            task_type_name,
            func_suffix):
        """Generates route method signature for the given route."""
        for name, _, typ in extra_args:
            route_args.append((name, typ))

        deprecated = 'DEPRECATED: ' if route.deprecated else ''

        func_name = '{}{}'.format(fmt_var(route.name), func_suffix)

        self.emit(comment_prefix)
        if route.doc:
            route_doc = self.process_doc(route.doc, self._docf)
        else:
            route_doc = 'The {} route'.format(func_name)
        self.emit_wrapped_text(
            deprecated + route_doc, prefix=comment_prefix, width=120)
        self.emit(comment_prefix)

        for name, doc in doc_list:
            self.emit_wrapped_text(
                '@param {} {}'.format(name, doc if doc else undocumented),
                prefix=comment_prefix,
                width=120)
        self.emit(comment_prefix)

func=self._cstor_name_from_fields(fields_no_default),
            args=self._cstor_args_from_fields(
                fields_no_default, is_struct=True),
            return_type='instancetype')

        self.emit(comment_prefix)
        description_str = (
            'Convenience constructor (exposes only non-nullable '
            'instance variables with no default value).')
        self.emit_wrapped_text(description_str, prefix=comment_prefix)
        self.emit(comment_prefix)
        for field in fields_no_default:
            doc = self.process_doc(field.doc,
                                   self._docf) if field.doc else undocumented
            self.emit_wrapped_text(
                '@param {} {}'.format(fmt_var(field.name), doc),
                prefix=comment_prefix)
        if struct.all_fields:
            self.emit(comment_prefix)
        self.emit_wrapped_text(
            '@return An initialized instance.', prefix=comment_prefix)
        self.emit(comment_prefix)

        self.emit('{};'.format(signature))
        self.emit()

def _docf(self, tag, val):
        if tag == 'route':
            return '`{}`'.format(fmt_func(val))
        elif tag == 'field':
            if '.' in val:
                cls_name, field = val.split('.')
                return ('`{}` in `{}`'.format(
                    fmt_var(field), self.obj_name_to_namespace[cls_name]))
            else:
                return fmt_var(val)
        elif tag in ('type', 'val', 'link'):
            return val
        else:
            return val

default_value = fmt_default_value(
                            field) if field.has_default else 'nil'
                        if is_primitive_type(data_type):
                            deserialize_call = '{} ?: {}'.format(
                                input_value, default_value)
                        else:
                            deserialize_call = '{} ? {} : {}'.format(
                                input_value, deserialize_call, default_value)

                    self.emit('{}{} = {};'.format(
                        fmt_type(field.data_type),
                        fmt_var(field.name), deserialize_call))

                self.emit()

                deserialized_obj_args = [(fmt_var(f.name), fmt_var(f.name))
                                         for f in struct.all_fields]
                init_call = fmt_func_call(
                    caller=fmt_alloc_call(caller=struct_name),
                    callee=self._cstor_name_from_fields(struct.all_fields),
                    args=fmt_func_args(deserialized_obj_args))
                self.emit('return {};'.format(init_call))

with self.block_func(
                        func=fmt_camel(field.name),
                        args=[],
                        return_type=fmt_type(field.data_type)):

                    with self.block(
                            'if (![self is{}])'.format(
                                fmt_camel_upper(field.name)),
                            delim=('{', '}')):
                        error_msg = 'Invalid tag: required {}, but was %@.'.format(
                            enum_field_name)
                        throw_exc = (
                            '[NSException raise:@"IllegalStateException" '
                            'format:@"{}", [self tagName]];')
                        self.emit(throw_exc.format(error_msg))
                    self.emit('return _{};'.format(fmt_var(field.name)))
                self.emit()

def _generate_struct_cstor_default(self, struct):
        """Emits struct convenience constructor. Default arguments are omitted."""
        if not self._struct_has_defaults(struct):
            return

        fields_no_default = [
            f for f in struct.all_fields
            if not f.has_default and not is_nullable_type(f.data_type)
        ]

        with self.block_func(
                func=self._cstor_name_from_fields(fields_no_default),
                args=fmt_func_args_from_fields(fields_no_default),
                return_type='instancetype'):
            args = ([(fmt_var(f.name), fmt_var(f.name) if not f.has_default and
                      not is_nullable_type(f.data_type) else 'nil')
                     for f in struct.all_fields])
            cstor_args = fmt_func_args(args)
            self.emit('return [self {}:{}];'.format(
                self._cstor_name_from_fields(struct.all_fields), cstor_args))
        self.emit()

deserialize_call = self._fmt_serialization_call(
                            field.data_type, input_value, False)

                    if nullable or field.has_default:
                        default_value = fmt_default_value(
                            field) if field.has_default else 'nil'
                        if is_primitive_type(data_type):
                            deserialize_call = '{} ?: {}'.format(
                                input_value, default_value)
                        else:
                            deserialize_call = '{} ? {} : {}'.format(
                                input_value, deserialize_call, default_value)

                    self.emit('{}{} = {};'.format(
                        fmt_type(field.data_type),
                        fmt_var(field.name), deserialize_call))

                self.emit()

                deserialized_obj_args = [(fmt_var(f.name), fmt_var(f.name))
                                         for f in struct.all_fields]
                init_call = fmt_func_call(
                    caller=fmt_alloc_call(caller=struct_name),
                    callee=self._cstor_name_from_fields(struct.all_fields),
                    args=fmt_func_args(deserialized_obj_args))
                self.emit('return {};'.format(init_call))

def _get_route_args(self, namespace, route, tag=False):  # pylint: disable=unused-argument
        """Returns a list of name / value string pairs representing the arguments for
        a particular route."""
        data_type, _ = unwrap_nullable(route.arg_data_type)
        if is_struct_type(data_type):
            arg_list = []
            for field in data_type.all_fields:
                arg_list.append((fmt_var(field.name), fmt_type(
                    field.data_type, tag=tag, has_default=field.has_default)))

            doc_list = [(fmt_var(f.name), self.process_doc(f.doc, self._docf))
                        for f in data_type.fields if f.doc]
        elif is_union_type(data_type):
            arg_list = [(fmt_var(data_type.name), fmt_type(
                route.arg_data_type, tag=tag))]

            doc_list = [(fmt_var(data_type.name),
                self.process_doc(data_type.doc,
                    self._docf) if data_type.doc
                else 'The {} union'.format(
                    fmt_class(data_type
                        .name)))]
        else:
            arg_list = []
            doc_list = []

        return arg_list, doc_list

def _get_default_route_args(
            self,
            namespace,  # pylint: disable=unused-argument
            route,
            tag=False):
        """Returns a list of name / value string pairs representing the default arguments for
        a particular route."""
        data_type, _ = unwrap_nullable(route.arg_data_type)
        if is_struct_type(data_type):
            arg_list = []
            for field in data_type.all_fields:
                if not field.has_default and not is_nullable_type(
                        field.data_type):
                    arg_list.append((fmt_var(field.name), fmt_type(
                        field.data_type, tag=tag)))

            doc_list = ([(fmt_var(f.name), self.process_doc(f.doc, self._docf))
                         for f in data_type.fields
                         if f.doc and not f.has_default and
                         not is_nullable_type(f.data_type)])
        else:
            arg_list = []
            doc_list = []

        return arg_list, doc_list