Re: [ANN] llua Higher-level C API for Lua

[Andrew Starks <andrew.starks@...>]

On Mon, Mar 10, 2014 at 11:46 AM, steve donovan
<steve.j.donovan@gmail.com> wrote:
> Hi all,
>
> There has been discussion recently about what extra goodies people
> would like to see in the C API, and so an experimental pre-release of
> llua [0] seems appropriate.  It's much like higher-level Lua bindings
> like luar [1] and LuaJava [2] - there are objects which represent Lua
> references, and they may be operated on directly, supporting the usual
> operations of indexing, calling and so forth.
>
> A related project is Selene [3], which exploits the very expressive
> syntactical sugar that C++ allows.  For C, we use the available
> mechanisms, such as varargs with argument type specifiers:
>
>     llua_t *G = llua_global(L);
>     llua_t *res = llua_gets(G,"print");
>     llua_callf(res,"ssi","one","two",42,"");
>
> These references are llib [4] objects, which are themselves
> reference-counted and have cleanup functions, so that unref(G) will
> remove the Lua reference as well as free the object.
>
> Multiple return values are handled in a similar way to input arguments:
>
>     llua_t *strfind = llua_gets(G,"string.find");
>     int i1,i2;
>     llua_callf(strfind,"ssi","hello dolly","doll",1,"ii",&i1,&i2);
>     printf("i1 %d i2 %d\n",i1,i2);
>
> Simplified ways to evaluate code and access table values:
>
>     llua_t *res = llua_eval(L,"return {a = 'one', b = 'two', c=66}","r");
>     char *av, *bv;
>     int cv;
>     double dv = 23.5;
>     llua_gets_v(res,
>         "a","s",&av,
>         "b","s",&bv,
>         "c","i",&cv,
>         "d","?f",&dv, // no error if not defined, use default!
>     NULL);
>     printf("got a='%s' b='%s' c=%d d=%f\n",av,bv,cv,dv);
>     //--> got a='one' b='two' c=66 d=23.500000
>
> There is some cost to this goodness, of course.  Using references is
> going to be a bit slower than explicit stack operations, but the idea
> here is to make it easier for relatively _casual_ use of the Lua API,
> or in places which are not speed critical.  On 32-bit Linux, my test
> programs are about 22Kb, so make it maybe an extra 14Kb overhead for
> statically linking in llua.
>
> The other cost is that as with any C API,  your foot is clearly marked
> with a target ;)
>
> llua has been tested for Lua 5.2 and 5.1, on Windows and Linux.  It
> currently compiles against the C99 standard, since life is too short
> sometimes.  With a project of this nature, it's not always clear how
> far to go, and what common patterns to support - which is why I
> decided for an early release.
>
> steve d.
>
>
> [0] https://github.com/stevedonovan/llua
> [1] https://github.com/stevedonovan/luar
> [2] https://github.com/jasonsantos/luajava
> [3] http://lua-users.org/lists/lua-l/2014-02/msg00077.html
> [4] https://github.com/stevedonovan/llib
>

See? This is exactly what I was hoping to get out of my post. :)

-Andrew