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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: Help requested with P99-based macro to create Wayland listeners
Date: Wed, 10 Apr 2024 19:56:36 -0700
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Blue-Maned_Hawk <bluemanedhawk@invalid.invalid> writes:

> This macro doesn't work and i don't know why.  I've tried multiple
> different things to try to delay the expansion of _0MAKE_LISTENER
> and none of them have worked.  I don't know if there's a more
> idiomatic way to do this.  I've tried looking at the output from
> putting it through ?cpp?  and that didn't work because it errored
> out before i could see what it expanded to.
>
> #define MAKE_LISTENER(object_type, ...) static const struct\
> object_type##_listener object_type##_listener = { P99_SEQ(\
> _0MAKE_LISTENER, P99_SEQ((object_type), __VA_ARGS__)) }
> #define _0MAKE_LISTENER(x) _1MAKE_LISTENER (x, _2MAKE_LISTENER
> #define _1MAKE_LISTENER _3MAKE_LISTENER
> #define _2MAKE_LISTENER(y) y)
> #define _3MAKE_LISTENER _4MAKE_LISTENER
> #define _4MAKE_LISTENER(object_type, event_name) .event_name =\
> callback_##object_type##_##event_name


After a lot of trial and error, I came up with the code below.
Probably it could be simplified, but I was happy just to get
it to work.


#include "p99.h"

#define static_const_LISTENER( kind, ... )  \
  static const PLAIN_LISTENER( kind, __VA_ARGS__ )

#define PLAIN_LISTENER( kind, ... )  \
  struct LISTENER_TAG_NAME( kind ) LISTENER_TAG_NAME( kind ) = {  \
    LISTENER_FIELDS( kind, __VA_ARGS__ )  \
  }

#define LISTENER_TAG_NAME( kind ) JOIN2( kind, _listener )

#define LISTENER_FIELDS( kind, ... )  \
  P99_SEQ( AS_IS,  \
    P99_SEQ( ONE_LISTENER_FIELD_2 AS_IS,  \
        P99_SEQ( ONE_LISTENER_FIELD, P99_SEQ( (kind), __VA_ARGS__ ) )  \
    )  \
  )

#define   ONE_LISTENER_FIELD( a )       ONE_LISTENER_FIELDx( a )
#define   ONE_LISTENER_FIELDx( a )      SINGLES_INTO_PAIR( a )

#define   SINGLES_INTO_PAIR( a_b )      ( ONE_COMMA_TWO a_b )
#define   ONE_COMMA_TWO( a )              a, AS_IS

#define   AS_IS( a )                    a

#define ONE_LISTENER_FIELD_2( a, b )  ONE_LISTENER_FIELD_2x( a, b )
#define ONE_LISTENER_FIELD_2x( kind, field )  \
  .field = callback_ ## kind ## _ ## field

#define JOIN2( a, b )   JOIN2x( a, b )
#define JOIN2x( a, b )  a ## b

static_const_LISTENER( wl_registry, global, global_remove );
static_const_LISTENER(
  xdg_wm_base,
  configure, close, configure_bounds, wm_capabilities
);