Lua 5.2 object - C ++ inside an object (using lua_lightuserdata)

Question

edit: [DECISION IN RESPONSE 2]

I am new to LUA and am having trouble trying to do what I want. I have a C ++ object that looks like this:

C ++ Object Definitions

struct TLimit
{
    bool   enabled;
    double value;

    TLimit() : enabled(false), value(0.0) {}
    ~TLimit() {}
};

class TMeaurement
{
public:
    TMeasurement() : meas(0.0) {}
    ~TMeasurement() {}

    TLimit min;
    TLimit max;
    double meas;
};

I want to be able in LUA to access an object of type TMeasurement in the following form:

LUA desired use

-- objmeas is an instance of TMeasurement
objmeas.min.enabled = true
print(objmeas.min.value);

... etc.

Another thing, I do not want LUA to allocate memory for an instance of an object of type TMeasurement. This will be done in my C ++ code. I tried many different things, all to no avail. I will send now the last of my attempts.

In my C ++ code, I defined the following:

TLimit - Get function that will be mapped to __index

#define LUA_MEAS_LIMIT    "itse.measurement.limit"

extern int llim_get(lua_State* L)
{
    TLimit*     lim = (TLimit*)lua_chekuserdata(L, 1, LUA_MEAS_LIMIT);
    std::string key = std::string(luaL_checkstring(L, 2));

    //-- this is only to check what is going on
    std::cout << "lim.get: " << key << std::endl;

    if(key.find("enabled") == 0)
        lua_pushboolean(L, lim->enabled);
    else if(key.find("value") == 0)
        lua_pushnumber(L, lim->value);
    else
        return 0;   //-- should return some sort of error, but let me get this working first

    return 1;
}

TLimit - Set the function to be displayed in __newindex

extern int llim_set(lua_State* L)
{
    TLimit*     lim = (TLimit*)lua_chekuserdata(L, 1, LUA_MEAS_LIMIT);
    std::string key = std::string(luaL_checkstring(L, 2));

    //-- this is only to check what is going on
    std::cout << "limit.set: " << key << " <-" << std::endl;

    if(key.find("enabled") == 0)
        lim->enabled = lua_toboolean(L, 3);
    else if(key.find("value") == 0)
        lim->value = lua_tonumber(L, 3);

    return 0;
}

TMeasurement. ( set "meas" ).

TMeasurement - Get __index

#define LUA_MEASUREMENT    "itse.measurement"

extern int lmeas_get(lua_State* L)
{
    TMeasurement* test = (TMeasurement*)lua_checkuserdata(L, 1, LUA_MEASUREMENT);
    std::string   key  = std::string(luaL_checkstring(L, 2));

    //-- this is only to check what is going on
    std::cout << "meas." << key << " ->" << std::endl;

    if(key.find("meas") == 0)
        lua_pushinteger(L, test->meas);
    else if(key.find("min") == 0)
    {
        lua_pushlightuserdata(L, &test->min);
        luaL_getmetatable(L, LUA_MEAS_LIMIT);
        lua_setmetatable(L, -2);
    }
    else if(key.find("max") == 0)
    {
        lua_pushlightuserdata(L, &test->max);
        luaL_getmetatable(L, LUA_MEAS_LIMIT);
        lua_setmetatable(L, -2);
    }
    else
        return 0;  //-- should notify of some error... when I make it work

    return 1;
}

, , mettatables :

++ -

( nsLUA:: safeFunction <... > , , < > " "... MessaegBox )

static const luaL_Reg lmeas_limit_f[] = { { NULL, NULL} };
static const luaL_Reg lmeas_limit[] =
{
        { "__index",    nsLUA::safeFunction<llim_get> },
        { "__newindex", nsLUA::safeFunction<lllim_set> },
        { NULL,      NULL }
};
//-----------------------------------------------------------------------------

static const luaL_Reg lmeas_f[] =  { { NULL, NULL} };
static const luaL_Reg lmeas[] =
{
        { "__index", nsLUA::safeFunction<lmeas_get> },
        { NULL,   NULL }
};
//-----------------------------------------------------------------------------

int luaopen_meas(lua_State* L)
{
    //-- Create Measurement Limit Table
    luaL_newmetatable(L, LUA_MEAS_LIMIT);
    luaL_setfuncs(L, lmeas_limit, 0);
    luaL_newlib(L, lmeas_limit_f);

    //-- Create Measurement Table
    luaL_newmetatable(L, LUA_MEASUREMENT);
    luaL_setfuncs(L, lmeas, 0);
    luaL_newlib(L, lmeas_f);

    return 1;
}

, ++ LUA, TMeasurement, LUA lua script. LEngine:

++ -

int main(int argc, char* argv[])
{
    if(argc < 2)
        return show_help();

    nsLUA::LEngine eng;

    eng.runScript(std::string(argv[1]));

    return 0;
}
//-----------------------------------------------------------------------------

int LEngine::runScript(std::string scrName)
{
    //-- This initialices LUA engine, openlibs, etc if not already done. It also
    //   registers whatever library I tell it so by calling appropriate "luaL_requiref"
    luaInit();

    if(m_lua)    //-- m_lua is the lua_State*, member of LEngine, and initialized in luaInit()
    {
        LMeasurement measurement;

        measurement.value = 4.5;   //-- for testing purposes

        lua_pushlightuserdata(m_lua, &tst);
        luaL_getmetatable(m_lua, LUA_MEASUREMENT);
        lua_setmetatable(m_lua, -2);
        lua_setglobal(m_lua, "step");

        if(luaL_loadfile(m_lua, scrName.c_str()) || lua_pcall(m_lua, 0, 0, 0))
            processLuaError();   //-- Pops-up a messagebox with the error
    }

    return 0;
}

, , . lua script, , memebr "min" "max" ... .

LUA -

print(step.meas);        -- Ok
print(step.min.enabled); -- Ok
print(step.min.enabled); -- Error: attempt to index field 'min' (a nil value)

, script:

                              first script line: print(step.meas);
meas.meas ->                     this comes from lmeas_get function
4.5                              this is the actual print from lua sentence
                              second script line: print(step.min.enabled)
meas.min ->                      accessing step.min, call to function lmeas_get
limit.get: enabled ->            accessing min.enabled, call to function llim_get
false                            actual print from script sentence
                              third script line: print(step.min.enabled)
limit.get: min ->                accessing min from limit object, call to llim_get ???????

. "min" ( "max", ), " ...". , __index ( e = step.min.enabled) __newindex (step.min.enabled = true).

, LUA min metatble . - "" " " LUA_MEASUREMENT metatable LUA_MEAS_LIMIT... .

, ... , ?

... , .

Answer 1

, lightuserdata (. ), lightuserdata . metatable lightuserdata, . :

• LEngine::runScript lightuserdata TMeasurement. step.
• step.min, lightuserdata TLimit ( lmeas_get). , step.min, step a TLimit,
• step.min , step TLimit, min nil.

Lightuserdata - . . , lightuserdata. . lightuserdata (, ), , .

, step userdata, TMeasurement. (. lua_setuservalue), . lmeas_get "min"/"max", uservalue . , userdata, - TLimit ( ), . , TLimit sub-userdata TMeasurement userdata, , , . uservalue.

Answer 2

, @siffiejoe @greatwolf . , , .

. , , . - , ./ ant , , .

-

LUA lightuserdata , , lightuserdata LUA, , LMetaPointer. __index __newindex LMetaPointer::__index LMetaPointer::__newindex. static std::map () LMetaPointer, - . , .

, lua __index __newindex, LMetaPointer::__index LMetaPointer::__newindex. , , get set, LMetaPointer.

, , LMetaPointer

. : LMetaPointer

//-----------------------------------------------------------------------------
#define LUA_METAPOINTER     "itse.metapointer"    //-- Name given to the metatable for all lightuserdata (instances of LMetaPointer in C++)
//-----------------------------------------------------------------------------

class LMetaPointer
{
private:
    static lua_State*                           m_lua;           //-- All LMetaPointers will share a common lua State
    static const luaL_Reg                       m_lmembers[];    //-- Member functions (for later expansion)
    static const luaL_Reg                       m_lfunctions[];  //-- Metamethods
    static std::map<LMetaPointer*, std::string> m_pointers;      //-- List of all LMetaPointer instances

    std::string m_name;                  //-- Name of LUA global variable pointing to me.

    static int __index(lua_State* L);    //-- Shall be mapped to __index metamethod of the metatable for all lightuserdata pointers
    static int __newindex(lua_State* L); //-- Shall be mapped to __newindex metamethod of the metatable for all lightuserdata pointers

    void initialize(lua_State* L);       //-- Creates the metatable (only once) and publishes it

protected:
public:
    LMetaPointer(lua_State* L);
    virtual ~LMetaPointer();

    inline lua_State*  lua()    { return m_lua;             }
    inline std::string global() { return m_name;            }
    inline size_t      size()   { return m_pointers.size(); }

    void setGlobal(std::string n);      //-- Shall make this pointer globally accessible to LUA

    virtual int get(lua_State* L) = 0;  //-- To be implemented by inherited classes
    virtual int set(lua_State* L) = 0;  //-- To be implemented by inherited classes

    LMetaPointer* operator [](std::string n);
};

//-----------------------------------------------------------------------------
#define lua_checkmpointer(L)    (LMetaPointer*)luaL_checkudata(L, 1, LUA_METAPOINTER)
//-----------------------------------------------------------------------------
lua_State* LMetaPointer::m_lua = NULL;
std::map<LMetaPointer*, std::string> LMetaPointer::m_pointers;
const luaL_Reg LMetaPointer::m_lmembers[]   = { { NULL, NULL } };
const luaL_Reg LMetaPointer::m_lfunctions[] =
{
        { "__index",    LMetaPointer::__index    },
        { "__newindex", LMetaPointer::__newindex },
        { NULL, NULL }
};
//-----------------------------------------------------------------------------

LMetaPointer::LMetaPointer(lua_State* L) : m_name("")
{
    //-- Make sure we have created the metatable
    initialize(L);

    //-- Add this pointer as of kind LUA_METAPOINTER metatable. This bit of code
    //   might not be necessary here. (To be removed)
    lua_pushlightuserdata(m_lua, this);
    luaL_getmetatable(m_lua, LUA_METAPOINTER);
    lua_setmetatable(m_lua, -2);

    //-- Add myself to the map of all metapointers
    m_pointers[this] = m_name;
}
//-----------------------------------------------------------------------------

LMetaPointer::~LMetaPointer()
{
    //-- Remove myself from the map of metapointers
    std::map<LMetaPointer*, std::string>::iterator found = m_pointers.find(this);

    if(found != m_pointers.end())
        m_pointers.erase(found);
}
//-----------------------------------------------------------------------------

int LMetaPointer::__index(lua_State* L)
{
    //-- Obtain the object that called us and call its get method.
    //   Since get and set are pure virtual, all inherited classes of LMetaPointer
    //   must implement it, and, upon the call from here, the correct 'get' method
    //   will be called.
    LMetaPointer* p = lua_checkmpointer(L);
    return p->get(L);
}
//-----------------------------------------------------------------------------

int LMetaPointer::__newindex(lua_State* L)
{
    //-- Obtain the object that called us and call its set method
    //   Since get and set are pure virtual, all inherited classes of LMetaPointer
    //   must implement it, and, upon the call from here, the correct 'get' method
    //   will be called.
    LMetaPointer* p = lua_checkmpointer(L);
    return p->set(L);
}
//-----------------------------------------------------------------------------

void LMetaPointer::initialize(lua_State* L)
{
    //-- Only create the metatable the first time and instance of LMetaPointer is created
    if(!m_lua)
    {
        m_lua = L;

        luaL_newmetatable(m_lua, LUA_METAPOINTER);
        luaL_setfuncs(L, m_lfunctions, 0);
        luaL_newlib(L, m_lmembers);
    }
}
//-----------------------------------------------------------------------------

void LMetaPointer::setGlobal(std::string n)
{
    //-- Make myself (this) a global variable in LUA with name given by 'n'
    std::map<LMetaPointer*, std::string>::iterator found = m_pointers.find(this);

    if(found != m_pointers.end())
    {
        m_name = n;
        found->second = m_name;

        lua_pushlightuserdata(m_lua, this);
        luaL_getmetatable(m_lua, LUA_METAPOINTER);
        lua_setmetatable(m_lua, -2);
        lua_setglobal(m_lua, m_name.c_str());
    }
}
//-----------------------------------------------------------------------------

LMetaPointer* LMetaPointer::operator [](std::string n)
{
    //-- Simply for completeness, allow all metapointer access all other by their
    //   name. (Notice though that since names are only assigned to instances made
    //   global, this operator will only work properly when searching for a pointer
    //   made global. ALl othe rpointers have an empty name.
    std::map<LMetaPointer*, std::string>::iterator iter = m_pointers.begin();

    while(iter != m_pointers.end())
    {
        if(iter->second == n)
            return iter->first;
        ++iter;
    }

    return NULL;
}

LUA (lightuserdata) . :

. LMeasLimit TLimit, LMeasurement - , LTest - TMeaasurement

-

//-------------------------------------------------------------------------

struct LMeasLimit : public LMetaPointer
{
    bool   enabled;     //-- Is the limit enabled?
    double value;       //-- Limit value;

    LMeasLimit(lua_State* L) : LMetaPointer(L), enabled(false), value(0.0) {}
    ~LMeasLimit() {}

    int get(lua_State* L);   //-- Implements LMetaPointer::get
    int set(lua_State* L);   //-- Implements LMetaPointer::set
};
//-------------------------------------------------------------------------

struct LMeasurement : public LMetaPointer
{
    double      value;      //-- Measurement
    LStepResult result;     //-- Result of test
    std::string message;    //-- Message to display

    LMeasurement(lua_State* L) : LMetaPointer(L), value(0.0), result(srNothing), message("") {}
    ~LMeasurement() {}

    int get(lua_State* L);   //-- Implements LMetaPointer::get
    int set(lua_State* L);   //-- Implements LMetaPointer::set
};
//-------------------------------------------------------------------------

struct LTest : public LMetaPointer
{
    int          id;    //-- ID of test
    std::string  name;  //-- Name of test
    LMeasLimit   max;   //-- Max limit for measure
    LMeasLimit   min;   //-- Min limit for measure
    LMeasurement meas;  //-- Measurement

    LTest(lua_State* L) : LMetaPointer(L), id(0), name(""), min(L), max(L), meas(L) {}
    ~LTest() {}

    int get(lua_State* L);   //-- Implements LMetaPointer::get
    int set(lua_State* L);   //-- Implements LMetaPointer::set
};

//-----------------------------------------------------------------------------

int LMeasLimit::get(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("enabled") == 0)
        lua_pushboolean(L, enabled);
    else if(key.find("value") == 0)
        lua_pushnumber(L, value);
    else
        return 0;

    return 1;
}
//-----------------------------------------------------------------------------

int LMeasLimit::set(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("enabled") == 0)
        enabled = lua_toboolean(L, 3);
    else if(key.find("value") == 0)
        value = lua_tonumber(L, 3);

    return 0;
}
//-----------------------------------------------------------------------------




int LMeasurement::get(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("value") == 0)
        lua_pushnumber(L, value);
    else if(key.find("result") == 0)
        lua_pushunsigned(L, result);
    else if(key.find("message") == 0)
        lua_pushstring(L, message.c_str());
    else
        return 0;

    return 1;
}
//-----------------------------------------------------------------------------

int LMeasurement::set(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("value") == 0)
        value = lua_tonumber(L, 3);
    else if(key.find("result") == 0)
        result = LStepResult(lua_tounsigned(L, 3));
    else if(key.find("message") == 0)
        message = std::string(lua_tostring(L, 3));

    return 0;
}
//-----------------------------------------------------------------------------



int LTest::get(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("id") == 0)
        lua_pushinteger(L, id);
    else if(key.find("name") == 0)
        lua_pushstring(L, name.c_str());
    else if(key.find("min") == 0)
    {
        lua_pushlightuserdata(L, &min);
        luaL_getmetatable(L, LUA_METAPOINTER);
        lua_setmetatable(L, -2);
    }
    else if(key.find("max") == 0)
    {
        lua_pushlightuserdata(L, &max);
        luaL_getmetatable(L, LUA_METAPOINTER);
        lua_setmetatable(L, -2);
    }
    else if(key.find("meas") == 0)
    {
        lua_pushlightuserdata(L, &meas);
        luaL_getmetatable(L, LUA_METAPOINTER);
        lua_setmetatable(L, -2);
    }
    else
        return 0;

    return 1;
}
//-----------------------------------------------------------------------------

int LTest::set(lua_State* L)
{
    std::string key = std::string(luaL_checkstring(L, 2));

    if(key.find("id") == 0)
        id = lua_tointeger(L, 3);
    else if(key.find("name") == 0)
        name = std::string(lua_tostring(L, 3));

    return 0;
}

- LEngine::runScript .

int LEngine::runScript(std::string scrName)
{
    luaInit();

    if(m_lua)
    {
        LTest tst(m_lua);

        tst.name = std::string("mierda_esta");
        tst.setGlobal("step");

        if(luaL_loadfile(m_lua, scrName.c_str()) || lua_pcall(m_lua, 0, 0, 0))
            processLuaError();
    }

    return 0;
}

, LUA, , .

- LUA script

print("step.id          = " .. step.id)
print("step.name        = " .. step.name)
print(step.min.enabled)
print("step.min.value   = " .. step.min.value)


step.id = 1
step.name = "nombre del test";
step.min.enabled = true;
step.min.value   = 5.6;

print("step.id          = " .. step.id)
print("step.name        = " .. step.name)
print(step.min.enabled)
print("step.min.value   = " .. step.min.value)

-

step.id          = 0
step.name        = mierda_esta
false
step.min.value   = 0
step.id          = 1
step.name        = nombre del test
true
step.min.value   = 5.6

, , . LMetaPointer, - , ++. .

@siffiejoe @greatwolf .