Re: Lua C API
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- Subject: Re: Lua C API
- From: Sean Conner <sean@...>
- Date: 2019年5月22日 16:45:44 -0400
It was thus said that the Great Jim once stated:
> On 5/17/19, William Ahern <william@25thandclement.com> wrote:
> > While the Lua C API has some unpleasant artifacts from incremental
> > improvements, it's actually much nicer than you seem to give it credit for.
> > And in my experience much nicer thanh the vast majority of APIs I've run
> > across.
>
> here is an example from the SGScript(.org) documentation:
> http://www.sgscript.org/pages/advdocs/sgscript.docs.htm#Argument-handling
>
> used in
> if ( sgs_LoadArgs ( "s|f", & str, & q ) ) return 0 ;
Shouldn't this be:
if (!sgs_LoadArgs("s|f",&str,&q)) return 0;
> sgs_LoadArgs() does type-based argument parsing
>
> 's' requires a value that can be converted to a string, returns to
> passed char**
> 'f' requires a value that can be converted to a real value, returns
> to passed float*
> '|' makes all arguments after it optional (always initialize data
> passed to those!)
>
> there are many more options and features for this function
I can only speak for myself, but the lack of this function hasn't bothered
me. For me, it's largely a difference of:
static int xdisplay_reparent(lua_State *L)
{
XReparentWindow(
*(Display **)lua_touserdata(L,1),
*(Window *)luaL_checkudata(L,2,TYPE_XWINDOW),
*(Window *)luaL_checkudata(L,3,TYPE_XWINDOW),
luaL_optinteger(L,4,0),
luaL_optinteger(L,5,0)
);
return 0;
}
vs (assuming Lua had a similar funtion):
static int xdisplay_reparent(lua_State *L)
{
Display *display;
Window w;
Window parent;
int x = 0;
int y = 0;
if (lua_loadargs(L,"ooo|ii",&display,&w,&parent,&x,&y))
XReparentWindow(display,w,parent,x,y);
else
luaL_error(L,"bad parameter to xdisplay_reparent()");
return 0;
}
It's not like I have tons of functions each with scores of parameters.
> Squirrel provides similar functionality (look it up yourself in its docs).
> this is just an example to show what other languages' C APIs provide.
>
> BTW:
>
> it is still not clear to me what a negative return value from a call to a
> Lua C function like "int cfunc ( lua_State * L )" means/represents/is used for.
The return value for a lua_CFunction is the number of returned
values---negative values are undefined behavior. For example, when I call
the following function:
int badret(lua_State *L)
{
return -lua_gettop(L);
}
I get:
> badret(1)
Segmentation fault (core dumped)
Your results may vary.
-spc (It's undefined!)