simple c++ binding ---- luna & lunar

相对于其他的一些 binding wrapper，luna 非常 light-weight，也是目前实际项目中选用 binding 方式。这里收集了 luna 相关的一些资料，备查。对于想了解 c++2lua binding 的林林总总，luna 也是一个最好的开始。

luna 绑定的 c++ class，有一个先决条件，就是此 c++ class 仅在 lua 中创建、使用、删除。
而 lunar 则对其作了些许扩展，让此 c++ class 的函数也能比较方便地在 c++ 中使用。

luna 的来源：
http://www.lua.org/notes/ltn005.html

lua 中 binding 一个 c++ class
http://lua-users.org/wiki/SimpleCppBinding

luna 的使用：
http://lua-users.org/wiki/SimplerCppBinding

lunar 的使用 (luna 的扩展)
http://lua-users.org/wiki/CppBindingWithLunar

使用 lunar 中的扩展功能（cpp 中调用 luna c++ class 的函数）
http://lua-users.org/wiki/CallingLuaFromCpp

luna.h for Lua 5.0

extern "C" {
#include "lua.h"
#include "lauxlib.h"
}

template <typename T> class Luna {
  typedef struct { T *pT; } userdataType;
public:
  typedef int (T::*mfp)(lua_State *L);
  typedef struct { const char *name; mfp mfunc; } RegType;

  static void Register(lua_State *L) {
    lua_newtable(L);
    int methods = lua_gettop(L);

    luaL_newmetatable(L, T::className);
    int metatable = lua_gettop(L);

    // store method table in globals so that
    // scripts can add functions written in Lua.
    lua_pushstring(L, T::className);
    lua_pushvalue(L, methods);
    lua_settable(L, LUA_GLOBALSINDEX);

    lua_pushliteral(L, "__metatable");
    lua_pushvalue(L, methods);
    lua_settable(L, metatable);  // hide metatable from Lua getmetatable()

    lua_pushliteral(L, "__index");
    lua_pushvalue(L, methods);
    lua_settable(L, metatable);

    lua_pushliteral(L, "__tostring");
    lua_pushcfunction(L, tostring_T);
    lua_settable(L, metatable);

    lua_pushliteral(L, "__gc");
    lua_pushcfunction(L, gc_T);
    lua_settable(L, metatable);

    lua_newtable(L);                // mt for method table
    int mt = lua_gettop(L);
    lua_pushliteral(L, "__call");
    lua_pushcfunction(L, new_T);
    lua_pushliteral(L, "new");
    lua_pushvalue(L, -2);           // dup new_T function
    lua_settable(L, methods);       // add new_T to method table
    lua_settable(L, mt);            // mt.__call = new_T
    lua_setmetatable(L, methods);

    // fill method table with methods from class T
    for (RegType *l = T::methods; l->name; l++) {
    /* edited by Snaily: shouldn't it be const RegType *l ... ? */
      lua_pushstring(L, l->name);
      lua_pushlightuserdata(L, (void*)l);
      lua_pushcclosure(L, thunk, 1);
      lua_settable(L, methods);
    }

    lua_pop(L, 2);  // drop metatable and method table
  }

  // get userdata from Lua stack and return pointer to T object
  static T *check(lua_State *L, int narg) {
    userdataType *ud =
      static_cast<userdataType*>(luaL_checkudata(L, narg, T::className));
    if(!ud) luaL_typerror(L, narg, T::className);
    return ud->pT;  // pointer to T object
  }

private:
  Luna();  // hide default constructor

  // member function dispatcher
  static int thunk(lua_State *L) {
    // stack has userdata, followed by method args
    T *obj = check(L, 1);  // get 'self', or if you prefer, 'this'
    lua_remove(L, 1);  // remove self so member function args start at index 1
    // get member function from upvalue
    RegType *l = static_cast<RegType*>(lua_touserdata(L, lua_upvalueindex(1)));
    return (obj->*(l->mfunc))(L);  // call member function
  }

  // create a new T object and
  // push onto the Lua stack a userdata containing a pointer to T object
  static int new_T(lua_State *L) {
    lua_remove(L, 1);   // use classname:new(), instead of classname.new()
    T *obj = new T(L);  // call constructor for T objects
    userdataType *ud =
      static_cast<userdataType*>(lua_newuserdata(L, sizeof(userdataType)));
    ud->pT = obj;  // store pointer to object in userdata
    luaL_getmetatable(L, T::className);  // lookup metatable in Lua registry
    lua_setmetatable(L, -2);
    return 1;  // userdata containing pointer to T object
  }

  // garbage collection metamethod
  static int gc_T(lua_State *L) {
    userdataType *ud = static_cast<userdataType*>(lua_touserdata(L, 1));
    T *obj = ud->pT;
    delete obj;  // call destructor for T objects
    return 0;
  }

  static int tostring_T (lua_State *L) {
    char buff[32];
    userdataType *ud = static_cast<userdataType*>(lua_touserdata(L, 1));
    T *obj = ud->pT;
    sprintf(buff, "%p", obj);
    lua_pushfstring(L, "%s (%s)", T::className, buff);
    return 1;
  }
};