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From: Ben Bacarisse <ben.usenet@bsb.me.uk>
Newsgroups: comp.lang.c
Subject: Re: Help requested with P99-based macro to create Wayland listeners
Date: Wed, 10 Apr 2024 15:49:09 +0100
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David Brown <david.brown@hesbynett.no> writes:

> 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

s/field/_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__) \
>     }

-- 
Ben.