用C语言编写OO-Lua接口的最佳方法?

考虑下面的例子(一个简单的二维向量库)。这里有一个构造函数函数,它用方法返回一个对象表。我对这种方法的问题是它正在用每个构造函数创建新表。是否有一种方法可以使用表的单个实例,但只更改标识方法正在处理的点的数据字段?这是更好的方法吗?

#include <stdlib.h>
#include <assert.h>
#include <stdio.h>
#include "lua.h"
#include "lauxlib.h"
#include "lualib.h"

const char* test = 
"p1 = point(410, 680);"
"p2 = point(320, 120);"
"print('dot='..p1:dot(p2));"
"print('cross='..p1:cross(p2));";

typedef struct point_t {
    lua_Number x, y;
} point_t;

point_t* p_new(lua_Number x, lua_Number y) {
    point_t* p = malloc(sizeof(point_t));
    p->x = x;
    p->y = y;
    return p;
}

void lua_settabledata(lua_State *L , char * key , void * value) {
    lua_pushstring(L, key);
    lua_pushlightuserdata(L, value);
    lua_settable(L, -3);
}

void lua_settablefunction(lua_State *L, char * key , lua_CFunction value) {
    lua_pushstring(L, key);
    lua_pushcfunction(L, value);
    lua_settable(L, -3);
}

point_t* lua_topoint(lua_State *L, int index) {
    point_t* p;
    lua_pushstring(L, "_data");
    lua_gettable(L, index);
    p = lua_touserdata(L, -1);
    lua_pop(L, 1);
    assert(p);
    return p;
}

int l_dot(lua_State *L) {
    point_t* p1 = lua_topoint(L, 1);
    point_t* p2 = lua_topoint(L, 2);
    lua_pushnumber(L, p1->x*p2->x + p1->y*p2->y);
    return 1;
}

int l_cross(lua_State *L) {
    point_t* p1 = lua_topoint(L, 1);
    point_t* p2 = lua_topoint(L, 2);
    lua_pushnumber(L, p1->x*p2->y - p1->y*p2->x);
    return 1;
}

int l_setx(lua_State *L) {
    point_t* p = lua_topoint(L, 1);
    p->x = lua_tonumber(L, 2);
    return 0;
}

int l_sety(lua_State *L) {
    point_t* p = lua_topoint(L, 1);
    p->y = lua_tonumber(L, 2);
    return 0;
}

int l_getx(lua_State *L) {
    point_t* p = lua_topoint(L, 1);
    lua_pushnumber(L, p->x);
    return 1;
}

int l_gety(lua_State *L) {
    point_t* p = lua_topoint(L, 1);
    lua_pushnumber(L, p->y);
    return 1;
}

int l_point(lua_State* L) {
    lua_Number x = lua_tonumber(L, 1);
    lua_Number y = lua_tonumber(L, 2);
    lua_newtable(L);
    lua_settabledata(L , "_data", p_new(x, y));
    lua_settablefunction(L , "dot", l_dot);
    lua_settablefunction(L , "cross", l_cross);
    lua_settablefunction(L , "setx", l_setx);
    lua_settablefunction(L , "sety", l_sety);
    lua_settablefunction(L , "getx", l_getx);
    lua_settablefunction(L , "gety", l_gety);
    return 1;
}

int main() {
    lua_State* L = lua_open();
    luaL_openlibs(L);
    lua_register(L, "point", l_point);
    if (luaL_loadstring(L, test) || lua_pcall(L, 0, 0, 0))
       printf("error: %s", lua_tostring(L, -1));
    getchar();
    return 0;
}