Re: Help requested with P99-based macro to create Wayland listeners

On 10/04/2024 16:26, Scott Lurndal wrote:

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
#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__) \
     }
>

>
Frankly I'd reject that code in any code review request.

 I normally like code to be so clear that comments about how it works are unnecessary.  But I think for something like this, a few comments would be helpful!
 When doing this kind of messing around with advanced preprocessing, it's useful to have a set of re-usable macros that can be written and documented once.  The "expand_macro_for_each" macro and its parts is partly there, and once that is in place and accepted, the rest is a lot smaller step to accept in a code review.
 But this is code to help the OP get his macro generations working. Whether he likes it, rejects it, or uses it for inspiration is up to him.