Aurélien Aptel <aurelien.aptel+emacs@gmail.com> schrieb am So., 4. Okt.
2015 um 23:12 Uhr:

> On Sun, Oct 4, 2015 at 9:47 PM, Philipp Stephani <p.stephani2@gmail.com>
> wrote:
> > Aurélien, is that something you agree with and could implement?
>
> I'm not sure I understood what you wanted.. I've commited this, but it
> assumes Lisp_Object are the same size as pointers...
>
> commit 4c2813950d14fa2348e30ee94a4f3b022263e36d
> Author: Aurélien Aptel <aurelien.aptel@gmail.com>
> Date:   Sun Oct 4 23:04:56 2015 +0200
>
>     use opaque struct emacs_value_tag instead of void* for emacs_value.
>
> diff --git a/src/emacs_module.h b/src/emacs_module.h
> index c5ec347..b055547 100644
> --- a/src/emacs_module.h
> +++ b/src/emacs_module.h
> @@ -27,7 +27,7 @@
>
>  /* Current environement */
>  typedef struct emacs_env_25 emacs_env;
> -typedef void* emacs_value;
> +typedef struct emacs_value_tag* emacs_value;
>
>  enum emacs_type {
>    EMACS_FIXNUM,
> diff --git a/src/module.c b/src/module.c
> index 9bbb832..ab058bb 100644
> --- a/src/module.c
> +++ b/src/module.c
> @@ -24,6 +24,8 @@
>  #include "dynlib.h"
>  #include "coding.h"
>
> +struct emacs_value_tag { Lisp_Object v; };
> +
>  void syms_of_module (void);
>  static struct emacs_runtime* module_get_runtime (void);
>  static emacs_env* module_get_environment (struct emacs_runtime *ert);
>


This is good (thanks!), but still assumes that sizeof(Lisp_Object) <=
sizeof(void*) and that (Lisp_Object)((void *)0) is never a valid Lisp
object, both of which are not provably true. To implement Daniel's approach
you'll also have to change:

static Lisp_Object value_to_lisp (emacs_value value) {
  return value->v;
}

static emacs_value lisp_to_value (Lisp_Object object) {
  emacs_value v = (emacs_value) malloc(sizeof v);
  // The allocation needs to be smarter, this example leaks memory.
  if (!v) return 0;
  v->v = object;
  return v;
}