注册一个C++类以在Lua 5.2中使用

Question

所以我正在阅读如何通过这个小博客教程为Lua创建和注册c ++类.

但是,尽管简单,信息丰富且易读,但它似乎是旧版本的Lua.

因此,某些功能/宏要么丢失,要么只有不同的签名.

在Lua C 5.2版中,以下代码是什么样的？

#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
#include <stringstream>
#include <string>

using namespace std;

// Just a useless test class
class MyClass
{
private:
    int _X;

public:
    MyClass(int x) : _X(x) {};
    ~MyClass() { Release() };

    // Displays your number in a welcoming message box
    void Hello()
    {
        stringstream ss;
        ss << "Hello!" << endl << "Your number is: " << _X;
        string s(ss.str());
        MessageBoxA(NULL, s.c_str(), "MyClass", MB_ICONINFORMATION);
    }

    void Release() {
        //release code goes here
    }
};

// Functions that will create/destroy MyClass instances
static int newMyClass(lua_State* L)
{
    int n = lua_gettop(L); // Number of arguments
    if (n != 2)
        return luaL_error(L, "Got %d arguments, expected 2 (class, x)", n);
    // First argument is now a table that represent the class to instantiate
    luaL_checktype(L, 1, LUA_TTABLE);

    lua_newtable(L); // Create table to represent instance

    // Set first argument of new to metatable of instance
    lua_pushvalue(L, 1);
    lua_setmetatable(L, -2);

    // Do function lookups in metatable
    lua_pushvalue(L, 1);
    lua_setfield(L, 1, "__index");

    // Allocate memory for a pointer to to object
    MyClass** s = (MyClass**)lua_newuserdata(L, sizeof(MyClass*));

    int x = luaL_checknumber(L, 2);

    *s = new MyClass(x);

    luaL_getmetatable(L, "Lua.MyClass");
    lua_setmetatable(L, -2);
    lua_setfield(L, -2, "__self");

    return 1;
}

static int doSomethingMyClass(lua_State* L)
{
    MyClass* c = nullptr;
    checkUserData(L, "Lua.MyClass", c);
    c->Hello();
    return 0;
}

static int destroyMyClass(lua_State* L)
{
    MyClass* c = nullptr;
    checkUserData(L, "Lua.MyClass", c);
    c->Release();
    return 0;
}

// Functions that will show up in our Lua environment
static const luaL_Reg gMyClassFuncs[] = {
    // Creation
    { "new", newMyClass) },
    { "hello", helloMyClass },
    { NULL, NULL }
};

static const luaL_Reg gDestroyMyClassFuncs[] = {
    {"__gc", destroyMyClass},
    {NULL, NULL}
};

// Registers the class for use in Lua
void registerMyClass(lua_State *L)
{  
    // Register metatable for user data in registry
    luaL_newmetatable(L, "Lua.MyClass");
    luaL_register(L, 0, gDestroyMyClassFuncs);      
    luaL_register(L, 0, gMyClassFuncs);      
    lua_pushvalue(L, -1);
    lua_setfield(L, -2, "__index");  

    // Register the base class for instances of Sprite
    luaL_register(L, "MyClass", gSpriteFuncs);  
}

基本上,这里的目标是能够在Lua中编写以下内容:

-- Create a new MyClass instance
local c = MyClass:new(5)
-- Show message
c:Hello() -- Should say something like "Hello! Your number is: 5"

为了使这项工作适用于5.2,我需要改变什么？

Answer 1

该代码中唯一不属于Lua 5.2的函数是luaL_register.你应该使用luaL_setfuncs.

您还应该MyClass手动设置全局或local MyClass=require"MyClass"在Lua代码中使用,因为require不再设置全局变量.

如果你正在嵌入Lua,你可以编译它和你的代码-DLUA_COMPAT_MODULE并获得5.1函数.但是,如果您计划使用此版本,请考虑现在是将代码移至Lua 5.2的好时机.