include/utils/Luna.h

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#ifndef LUNA_H_
#define LUNA_H_

/*****************************************************************************
 *     .:: Luna ::.                                                          *
 *                                                                *   , *    *
 *  C++ library for binding classes into Lua.     By nornagon.       ((   *  *
 *                                                               *    `      *
 *  Example:                                                                 *
 *****************************************************************************

    class Foo {
      public:
        Foo(lua_State *L) {
          printf("in constructor\n");
        }

        int foo(lua_State *L) {
          printf("in foo\n");
        }

        ~Foo() {
          printf("in destructor\n");
        }

        static const char className[];
        static const Luna<Foo>::RegType Register[];
    };

    const char Foo::className[] = "Foo";
    const Luna<Foo>::RegType Foo::Register[] = {
      { "foo", &Foo::foo },
      { 0 }
    };

 *****************************************************************************
 * Then:                                                                     *
 *****************************************************************************

    Luna<Foo>::Register(L);

 *****************************************************************************
 * From Lua:                                                                 *
 *****************************************************************************

    local foo = Foo()
    foo:foo()

 *****************************************************************************
 * Clean up:                                                                 *
 *****************************************************************************

    lua_close(L);

 *****************************************************************************
 * Output:                                                                   *
 *****************************************************************************

    in constructor
    in foo
    in destructor

 *****************************************************************************
 * This program is free software. It comes without any warranty, to          *
 * the extent permitted by applicable law. You can redistribute it           *
 * and/or modify it under the terms of the Do What The Fuck You Want         *
 * To Public License, Version 2, as published by Sam Hocevar. See            *
 * http://sam.zoy.org/wtfpl/COPYING for more details.                        *
 ****************************************************************************/

#ifdef HAVE_LIBLUA5_1

// convenience macros
#define luna_register(L, klass) (Luna<klass>::Register((L)))
#define luna_registermetatable(L, klass) (Luna<klass>::RegisterMetatable((L)))
#define luna_inject(L, klass, t) (Luna<klass>::inject((L), (t)))

extern "C" {
#include "lua5.1/lua.h"
#include "lua5.1/lualib.h"
#include "lua5.1/lauxlib.h"
}

template<class T> class Luna {
  public:
    static void Register(lua_State *L) {
      lua_pushcfunction(L, &Luna<T>::constructor);
      lua_setglobal(L, T::className); // T() in lua will make a new instance.

      RegisterMetatable(L);
    }

    // register the metatable without registering the class constructor
    static void RegisterMetatable(lua_State *L) {
      luaL_newmetatable(L, T::className); // create a metatable in the registry
      lua_pushstring(L, "__gc");
      lua_pushcfunction(L, &Luna<T>::gc_obj);
      lua_settable(L, -3); // metatable["__gc"] = Luna<T>::gc_obj
      lua_pop(L, 1);
    }

    static int constructor(lua_State *L) {
      return inject(L, new T(L));
    }

    static int inject(lua_State *L, T* obj) {
      lua_newtable(L); // create a new table for the class object ('self')

      lua_pushnumber(L, 0);

      T** a = static_cast<T**>(lua_newuserdata(L, sizeof(T*))); // store a ptr to the ptr
      *a = obj; // set the ptr to the ptr to point to the ptr... >.>
      luaL_newmetatable(L, T::className); // get (or create) the unique metatable
      lua_setmetatable(L, -2); // self.metatable = uniqe_metatable

      lua_settable(L, -3); // self[0] = obj;

      for (int i = 0; T::Register[i].name; i++) { // register the functions
        lua_pushstring(L, T::Register[i].name);
        lua_pushnumber(L, i); // let the thunk know which method we mean
        lua_pushcclosure(L, &Luna<T>::thunk, 1);
        lua_settable(L, -3); // self["function"] = thunk("function")
      }
      return 1;
    }

    static int thunk(lua_State *L) {
      // redirect method call to the real thing
      int i = (int)lua_tonumber(L, lua_upvalueindex(1)); // which function?
      lua_pushnumber(L, 0);
      lua_gettable(L, 1); // get the class table (i.e, self)

      T** obj = static_cast<T**>(luaL_checkudata(L, -1, T::className));
      lua_remove(L, -1); // remove the userdata from the stack

      return ((*obj)->*(T::Register[i].mfunc))(L); // execute the thunk
    }

    static int gc_obj(lua_State *L) {
      // clean up
      //printf("GC called: %s\n", T::className);
      T** obj = static_cast<T**>(luaL_checkudata(L, -1, T::className));
      delete (*obj);
      return 0;
    }

    struct RegType {
      const char *name;
      int(T::*mfunc)(lua_State*);
    };
};

#endif
#endif /* LUNA_H_ */

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