file.c:2484
static VALUE
rb_stat_W(obj)
    VALUE obj;
{
    struct stat *st = get_stat(obj);

#ifdef S_IWUSR
    if (rb_stat_rowned(obj))
	return st->st_mode & S_IWUSR ? Qtrue : Qfalse;
#endif
#ifdef S_IWGRP
    if (group_member(get_stat(obj)->st_gid))
	return st->st_mode & S_IWGRP ? Qtrue : Qfalse;
#endif
#ifdef S_IWOTH
    if (!(st->st_mode & S_IWOTH)) return Qfalse;
#endif
    return Qtrue;
}
