Question

I notice that in the generated SWIG wrappers for a given set of classes, SWIG keeps a list of C-string representations of all the parent classes from which that class inherits. (char ** base_names). I know there is a function

swig_type(some_variable)

that will return a string representation of a given variable’s data type. Is there also a function that will return a table of the parent classes as strings? If not, is there an easy way to write this function? I’m not at all familiar with the inner workings of SWIG.

Thanks!

Answer 1

Something like this should work (not tested, since I don’t use SWIG with Lua):

// insert into runtime section
// this is the C function that iterates over the base_names array 
// (I'm assuming that the array is terminated with a NULL)
%runtime %{
    /* lua callable function to get the userdata's type */
    SWIGRUNTIME int SWIG_Lua_basenames(lua_State* L)
    {
      swig_lua_userdata* usr;
      swig_lua_class* clss = NULL;
      int i = 0;
      if (lua_isuserdata(L,1))
      {
        usr=(swig_lua_userdata*)lua_touserdata(L,1);  /* get data */
        if (usr && usr->type && usr->type->clientdata) {
          // fetch the swig_lua_class struct, it contains the base_names
          clss = (swig_lua_class*)usr->type->clientdata;
        }
      }
      /* create a new table with all class base names in it
         note that I create it even if clss is NULL, that way
         an empty table -should- be returned
       */          
      lua_newtable(L);
      while(clss && clss->base_names[i]) {
         lua_pushnumber(L, i+1); /* lua tables are 1-indexed */
         lua_pushstring(L, clss->base_names[i]);
         lua_rawset(L, -3);
         i++;
      }
      return 1;
    }
%}
%init %{
  /* this goes into the user init function, register our new function with
     Lua runtime
   */
  SWIG_Lua_add_function(L,"swig_base_names",SWIG_Lua_basenames);
%}