使用 "get"方法的 C++ 类继承

Question

我想创建一个主要包含静态成员/方法的基类，例如:

class LuaObject {
    public:
        static const luaL_Reg Methods[];

        static int Create(lua_State *L);

        static LuaObject* get(lua_State *L, int pos) {
            return *(LuaObject**)luaL_checkudata(L, pos, LuaObject::Metatable);
        }
};

然后针对特定类型的对象从中派生:

class Pulse: public LuaObject {
    public:
        int n;
    //...
};

const luaL_Reg Pulse::Methods[] = {
    //...
};

static int Pulse::Create(lua_State *L) {
    Pulse **ud = (Pulse**)lua_newuserdata(L, sizeof(Pulse*));
    *ud = new Pulse();
    //...
}

但是，如果不进行大量复制和粘贴(违背 LuaObject 的目的)，我不确定如何解决这个问题。出现两个问题:

1. 我收到如下错误:error: ISO C++ does not permit 'LuaObject::Methods' to be defined as 'Pulse::Methods' [-fpermissive] 和 错误:没有在类“Pulse”中声明“int Pulse::Create(lua_State*)”成员函数。也就是说，Pulse 似乎没有从 LuaObject 继承静态成员/方法。

2. get(L, n) 方法旨在返回指向类实例的指针，例如我希望能够写:

   Pulse *p = Pulse::get(L,1);printf("p->n = %d\n", p->n);

   However, it seems like since get is only defined for LuaObject, I'd get a LuaObject*, not a Pulse*.

How can I address these issues without having to copy Methods, Create, get etc into Pulse (and all other classes derived from LuaObject)?
I thought turning it into a template might help:

template <class T>
class LuaObject {
    public:
        static const luaL_Reg Methods[];

        static int Create(lua_State *L);

        static T* get(lua_State *L, int pos) {
            return *(T**)luaL_checkudata(L, pos, T::Metatable);
        }
};

class Pulse: public LuaObject<Pulse> {
    public:
        //...
};

但即使这样也会出现同样的错误，所以我很困惑。

编辑:根据要求，一个最小的示例程序，包括编译错误:(使用 g++ test.cpp -Llua -Lpulse -o test 构建)

#include <stdio.h>
#include <stdlib.h>
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>
#include <pulse/pulseaudio.h>

class LuaObject {
    public:
        static const char *Metatable;
        static const luaL_Reg Methods[];

        static void InitModule(lua_State *L);
        static int Create(lua_State *L);

        //Retrieve object instance from Lua stack at specified position
        static LuaObject* get(lua_State *L, int pos) {
            return *(LuaObject**)luaL_checkudata(L, pos, LuaObject::Metatable);
        }
};


class Pulse: public LuaObject {
    //Here I want to avoid having to declare/define Metatable, get() etc again.
    public:
        static int getEvent(lua_State *L);
        pa_context *ctx;
};



const char *Pulse::Metatable = "pulse"; //error: ISO C++ does not permit ‘LuaObject::Metatable’ to be defined as ‘Pulse::Metatable’ [-fpermissive]
const luaL_Reg Pulse::Methods[] = { //error: ISO C++ does not permit ‘LuaObject::Methods’ to be defined as ‘Pulse::Methods’ [-fpermissive]
    {"getEvent", Pulse::getEvent},
    {NULL, NULL}
};


//Set up the "pulse" module in a Lua state
static void Pulse::InitModule(lua_State *L) { //error: no ‘void Pulse::InitModule(lua_State*)’ member function declared in class ‘Pulse’
    if(luaL_newmetatable(L, Pulse::Metatable)) {
        luaL_setfuncs(L, Pulse::Methods, 0);
    }
    lua_pop(L, 1); //remove metatable from Lua stack, leave in Lua registry

    static luaL_Reg lib[] = {
        {"new", Pulse::Create},
        {NULL, NULL}
    };
    luaL_newlibtable(L, lib);
    lua_setglobal(L, "pulse");
}

//Called from Lua (as pulse.new()) to create a Pulse object
static int Pulse::Create(lua_State *L) { //error: no ‘int Pulse::Create(lua_State*)’ member function declared in class ‘Pulse’
    Pulse **ud = (Pulse**)lua_newuserdata(L, sizeof(Pulse*));
    *ud = new Pulse();
    return 1;
}


//Called from Lua (as myPulse:getEvent()) to read events
int Pulse::getEvent(lua_State *L) {
    //We only have L as parameter; the Pulse object is on the Lua stack,
    //so we need to read it using luaL_checkudata() (which is handled
    //by get())
    Pulse *self = Pulse::get(L, 1); //error: invalid conversion from ‘LuaObject*’ to ‘Pulse*’ [-fpermissive]

    //pretend get_pulse_event() is defined in pulseaudio.h (the actual mechanism
    //is much more complex and wouldn't help the example)
    int event = get_pulse_event(self->ctx);
    lua_pushinteger(L, event);
    return 1;
}


int main(int argc, char **argv) {
    lua_State *L = luaL_newstate();
    luaL_openlibs(L);
    Pulse::InitModule(L);
    return luaL_dofile(L, "main.lua");
}

Answer 1

必须为 base 定义来自 base 的静态成员。如果你想为派生类定义它们，你必须再次声明它们。这并不意味着您无法访问派生的静态成员，尽管您必须知道不能将静态成员声明为 virtual

顺便说一句:static 只能在类定义中指定。