Re: C++ creation of object, and Lua co-calling

[Gary Makin <garym@...>]

You're right there. I'm using the ID field in the table to get to the C++
object, but that's because I'm using STL, and it encourages copying objects
around and not using pointers.

If you are using pointers, it would be easy enough to stick the pointer as a
userdata in the table, and to use that. Once you did, the static routine
would be able to access all the fields in the class (as it's a member of the
class and has access privileges) but you'd need to preface them all with
object->


On 17/6/02 17:52, "Robert Sadedin" <serenity@nosubstancesoftware.com> wrote:

> What's the advantage of using this method over exposing straight functions?
> Or have I got something very wrong?
> A static member function can't access the variables within a class, so with
> my limited understanding this doesn't seem to help expose the methods of the
> c++ object?
> I do rather think I am wrong though :).
> 
> ----- Original Message -----
> From: "Gary Makin" <garym@ssg.com.au>
> To: "Multiple recipients of list" <lua-l@tecgraf.puc-rio.br>
> Sent: Monday, June 17, 2002 5:50 PM
> Subject: Re: C++ creation of object, and Lua co-calling
> 
> 
>> I think this answers the question you're asking:
>> 
>> The C++ function you make available to Lua must be a static member
> function.
>> I really should have mentioned this. In Lua, I call the function using the
> :
>> operation, so it sticks a copy of the object on the stack. From that I
> grab
>> the ID, and that allows me to get at the C++ object.
>> 
>> Gary
>> 
>> 
>> On 17/6/02 17:08, "Robert Sadedin" <serenity@nosubstancesoftware.com>
> wrote:
>> 
>>> Hmmm.  Interesting, and cool.  How do you store a reference to the
> methods
>>> in a class?
>>> I can store a pointer to an object no sweat, but I don't know how to
> call a
>>> method relating to that object without adding to lua to handle pointers
> to a
>>> specific class method.
>>> 
>>> ----- Original Message -----
>>> From: "Gary Makin" <garym@ssg.com.au>
>>> To: "Multiple recipients of list" <lua-l@tecgraf.puc-rio.br>
>>> Sent: Monday, June 17, 2002 1:33 PM
>>> Subject: Re: C++ creation of object, and Lua co-calling
>>> 
>>> 
>>>> I think the solution depends on just what you want to do. For my
> project,
>>>> I've decided to forego using tolua, and to do it all manually.
>>>> 
>>>> I've got a bunch of different C++ classes, and objects of those
> classes,
>>> and
>>>> I wanted to have parallel objects available in Lua. I ended up putting
> a
>>>> routine in each class to create the Lua object for each C++ object.
>>>> 
>>>> The code creates a new Lua table, and gets a reference to it (telling
> Lua
>>>> not to garbage collect the table). The reference is stored in the C++
>>>> object, and I use that whenever C++ needs to access Lua.
>>>> 
>>>> In the Lua table I've added a read-only ID entry that I use to find the
>>> C++
>>>> object (I'm using STL, so pointers and iterators aren't always safe to
>>>> store).
>>>> 
>>>> For each method, or data item, that I want to have accessible from Lua,
>>> I've
>>>> added a table entry for the C++ routine. Of course, these C++ routines
>>> need
>>>> different parameters than a C++ only routine would need, so I've tended
> to
>>>> end up with two versions of a lot of the routines, with one calling the
>>>> other.
>>>> 
>>>> I've also added some inheritance, so I'm making a single table that's
> the
>>>> parent for all the tables of one class. For example, I've got one
> master
>>>> Ruin table that is the parent for all the Ruin tables that represent
> real
>>>> Ruins in the game. I've added all the common methods to the parent
> Ruin,
>>> so
>>>> I don't need to have copies of all the functions in all the ruins, or
>>> copies
>>>> of pointers for C++ functions (as I'm using Lua functions to be called
> fro
>>> m
>>>> Lua whenever possible).
>>>> 
>>>> As a caveat, I've only got this working in the last week, so I don't
> have
>>> a
>>>> fully working game using this, but it seems like the system will hold
> up.
>>>> 
>>>> Gary Makin
>>>> Lead Programmer
>>>> Strategic Studies Group
>>>> 
>>>> 
>>>> On 17/6/02 6:55, "Robert Sadedin" <serenity@nosubstancesoftware.com>
>>> wrote:
>>>> 
>>>>> For my game scripting, I need to be able to expose methods from
> objects
>>>>> created in my c++ class to Lua.
>>>>> 
>>>>> I know there are a number of solutions for providing c++ classes in
> lua
>>> so
>>>>> long as they are created in Lua, but what about when the construction
> is
>>> in
>>>>> the host application?
>>>>> 
>>>>> Essentially, I need method sharing with the creation process being
>>>>> consumated by the c++ app.
>>>>> 
>>>>> What is the simplest, and least ambitious method for doing this that
> you
>>>>> experts can think of?
>>>>> 
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> 
>>>>> 
>>>>> Rob
>>>>> 
>>>> 
>>> 
>> 
>