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From: David Brown <david.brown@hesbynett.no>
Newsgroups: comp.lang.c
Subject: Re: Help requested with P99-based macro to create Wayland listeners
Date: Wed, 10 Apr 2024 11:05:55 +0200
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On 09/04/2024 22:20, Blue-Maned_Hawk wrote:
> David Brown wrote:
> 
>> On 09/04/2024 20:17, Blue-Maned_Hawk wrote:
>>> Tim Rentsch wrote:
>>>
>>>> What is it that you want to accomplish?
>>>
>>> As i stated in the subject line, i am trying to create a macro to
>>> create Wayland listeners.
>>>
>>>
>> Assume, for the sake of argument, that no one knows or cares anything
>> about Wayland or listeners.
> 
> <https://xkcd.com/1432/>
> 
>> You are trying to use a set macros to expand to some code.  Start by
>> showing what code you want to get from examples of using your macros -
>> then people can try to help get the macros right.
> 
> MAKE_LISTENER(wl_registry, global, global_remove);
> 
> →
> 
> static const struct wl_registry_listener wl_registry_listener = { .global
> = callback_wl_registry_global, .global_remove =
> callback_wl_registry_global_remove };

#define _get_6th_arg(_1, _2, _3, _4, _5, _arg, ...) _arg
#define _fe_0(_global, _call, ...)
#define _fe_1(_global, _call, x) _call(_global, x)
#define _fe_2(_global, _call, x, ...) _call(_global, x) _fe_1(_global, 
_call, __VA_ARGS__)
#define _fe_3(_global, _call, x, ...) _call(_global, x) _fe_2(_global, 
_call, __VA_ARGS__)
#define _fe_4(_global, _call, x, ...) _call(_global, x) _fe_3(_global, 
_call, __VA_ARGS__)
#define expand_macro_for_each(_global, _macro, ...) \
     _get_6th_arg("ignored", __VA_ARGS__, \
     _fe_4, _fe_3, _fe_2, _fe_1, _fe_0)(_global, _macro, __VA_ARGS__)



#define MAKE_LISTENER(object_type, ...) _make_listener(object_type, 
__VA_ARGS__)
#define _listener_entry(_global, _field) , . _field = callback_ ## 
_global ## _ ## field
#define _make_listener(object_type, first_field, ...) static const struct \
     object_type ## _listener object_type ## _listener = { \
     .first_field = callback_ ## object_type ## _ ## first_field \
     expand_macro_for_each(object_type, _listener_entry, __VA_ARGS__) \
     }