我正在尝试用 C 语言进行面向对象,并希望有一个用于表示法的语法糖宏
object->vtable->method(object, arg1, arg2)
into
send(object, method, arg1, arg2)
不幸的是,当一个方法不带参数时,就会出现尾随逗号问题
send(object, method)
gives
object->vtable->method(object, )
有没有portable (no ##__VA_ARGS__
或 Visual Studio)这样做的方式?
我想出了一个,但我需要交换对象和方法
#define FIRST_ARG_(N, ...) N
#define FIRST_ARG(args) FIRST_ARG_(args)
#define send(msg, ...) \
FIRST_ARG(__VA_ARGS__)->vtable->msg(__VA_ARGS__)
permits
send(method, object)
send(method, object, arg1, arg2)
Edit
在下面两个好的答案的帮助下,我将使用这些宏来完成此操作。它最多可处理 16 个参数,但可以轻松扩展
#define SEND_NO_ARG(obj, msg) obj->vtable->msg(obj)
#define SEND_ARG(obj, msg, ...) obj->vtable->msg(obj, __VA_ARGS__)
#define GET_18TH_ARG(arg1, arg2, arg3, arg4, arg5, \
arg6, arg7, arg8, arg9, arg10, arg11, arg12, arg13, arg14, arg15, \
arg16, arg17, arg18, ...) arg18
#define SEND_MACRO_CHOOSER(...) \
GET_18TH_ARG(__VA_ARGS__, \
SEND_ARG, SEND_ARG, SEND_ARG, SEND_ARG, SEND_ARG, \
SEND_ARG, SEND_ARG, SEND_ARG, SEND_ARG, SEND_ARG, \
SEND_ARG, SEND_ARG, SEND_ARG, SEND_ARG, SEND_ARG, \
SEND_NO_ARG, )
#define SEND(...) SEND_MACRO_CHOOSER(__VA_ARGS__)(__VA_ARGS__)