The-Powder-Toy/src/cat/LuaLuna.h

#pragma once
//http://lua-users.org/wiki/SimplerCppBinding

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
	}

	static void * tryGet(lua_State * L, int narg)
	{
		if(checkType(L, narg, T::className))
		{
			userdataType *ud = static_cast<userdataType*>(luaL_checkudata(L, narg, T::className));
			if(!ud)
				luaL_typerror(L, narg, T::className);
			return ud;  // pointer to T object
		}
		else
		{
			return NULL;
		}
	}

	static bool checkType (lua_State * L, int idx, const char *name) 
	{
		// returns true if a userdata is of a certain type
		int res;
		if (lua_type(L, idx) != LUA_TUSERDATA) return false;
		lua_getmetatable(L, idx);
		luaL_newmetatable (L, name);
		res = lua_equal(L, -2, -1);
		lua_pop(L, 2); // pop both tables (metatables) off
		return res;
	}

	static inline T * get(void * userData)
	{
		return ((userdataType*)userData)->pT;
	}

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
		
		obj->UserData = luaL_ref(L, LUA_REGISTRYINDEX);
		lua_rawgeti(L, LUA_REGISTRYINDEX, obj->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;
	}
};