Re: Should we explicitly cast from luaL_checkinteger() et al?

[Philipp Janda <siffiejoe@...>]

Am 23.01.2015 um 04:37 schröbte William Ahern:
> On Fri, Jan 23, 2015 at 01:05:48AM +0200, Niccolo Medici wrote:
> <snip>
> > Lua 5.3 deprecates luaL_checkint, luaL_checklong, luaL_optint,
> > luaL_optlong, which were just convenience macros calling
> > luaL_{check|opt}integer.
> >
> > While we can still use them (because of -DLUA_COMPAT_5_2), they aren't
> > mentioned in the user manual and we're advised to use
> > luaL_{check|opt}integer "with a type cast".
>
> [...]
>
> > (2) If a cast isn't needed here, where *is* it needed?
>
> Assuming an architecture where sizeof (int) < sizeof (lua_Integer), then the
> following would print two different results:
>
>      printf("%zu\n", sizeof luaL_checkinteger(0, 0));
>      printf("%zu\n", sizeof ((int)luaL_checkinteger(0, 0)));

I'll throw in two more examples:

    printf("%d\n", (int)luaL_checkinteger(L, 1));

(undefined behavior without the cast)

or:

    lua_Integer x = 0U + (int)luaL_checkinteger(L, 1);

(with cast: 0 <= x <= UINT_MAX, without cast: LUA_MININTEGER <= x <= 
LUA_MAXINTEGER)

> <snip>
> > (4) Aren't we losing "documentation" by not having the words
> > "int"/"long" embedded in the function name?

The "int"/"long" is embedded in the cast instead, which is a normal 
place for C programmers to look. Actually, we *gain* documentation, 
because we have the target type *and* the internal Lua type mentioned 
explicitly in the code.


Philipp