Re: Calling overloaded original functions

["Greg Falcon" <veloso@...>]

On Thu, May 8, 2008 at 4:31 PM, Till Harbaum / Lists <lists@harbaum.org> wrote:
> How is this done? And perhaps someone even knows how to do this from
> a c function?
>
> lua_pushcfunction(L, my_tostring);
> lua_setfield(L, LUA_GLOBALSINDEX, "tostring");
>
> Overwrites tostring, but how do i call the original function from my "my_tostring"?

To do the equivalent thing from the C API, instead of
lua_pushcfunction, use lua_pushcclosure.  The latter takes an extra
integer argument, the number of values to pop off the stack and store
in the function object that gets created.  So:

  lua_getglobal(L, "tostring");
  lua_pushcclosure(L, my_tostring, 1);
  lua_setglobal(L, "tostring");

Then, inside my_tostring, you can access the original tostring
function with the pseudo index lua_upvalueindex(1).

That is, where you would have written
  lua_getglobal(L, "tostring");
to access the original function object, you instead can write
  lua_pushvalue(L, lua_upvalueindex(1));

Greg F