Re: Copying a container on function call... (Was Re: return_stl_iterator acting as const?)

Well another 2 days on this and still no closer to figuring it out...  I
tried to wrap a custom iterator around the class:

typedef std::vector<ContainedObject> ContainedObjectVec;

class ContainedObjectVectorIterator
{
public:
    ContainedObjectVectorIterator(ContainedObjectVec* pVec)
        : m_pVec(pVec)
    {
    }

    struct iterator : boost::iterator_adaptor<iterator, ContainedObject*>
    {
        iterator(ContainedObject* p) : iterator::iterator_adaptor_(p)
        {

        }

        iterator(iterator const& other) : iterator::iterator_adaptor_(other)
        {

        }
    };

    iterator begin()
    {
        return iterator( m_pVec->begin()._Myptr );
    }

    iterator end()
    {
        return iterator( m_pVec->end()._Myptr);
    }

    ContainedObjectVec* m_pVec;
};

made that a member variable of ContainerObject and still the same result.

I'm really amazed that it is so difficult, and no one seems to know how to
pass a vector of objects to LUA and have LUA modify member variables of
those objects.  It would seem to be the type of problem that luabind was be
designed to solve.  However every example I can find on the web, the only
use of a container of objects is to read the values not modify them.  So I'm
completely at a loss here...


On Tue, Mar 3, 2009 at 10:49 PM, John Smith <[email protected]> wrote:

> So I'm still having a problem with this, looking into it more it seems that
> the problem is the Copy Construct is being called via:
>
> server.exe!luabind::detail::value_converter::apply<ContainedObject>(lua_State
> * L=0x00f45ca8, const ContainedObject& ref={...})  Line 299 + 0x2f bytes
> C++
>      server.exe!luabind::detail::convert_to_lua<ContainedObject>(lua_State
> * L=0x00f45ca8, const ContainedObject& v={...})  Line 74    C++
>
> server.exe!luabind::detail::iterator<std::_Vector_iterator<ContainedObject,std::allocator<ContainedObject>
> > >::next(lua_State * L=0x00f45ca8)  Line 24 + 0x12 bytes    C++
> specifically:
> object_ptr = new T(ref);
>
> So we're deffinetly making a copy of the vector when we go into the
> function exec.  Is there anyway to specify to pass the member variable by
> reference and not by copy?  Due to some constraints of other APIs I'm using,
> I have to store some objects I'm trying to expose to lua in the container, I
> can't just pass them by a pointer.
>
> Any thoughts as to things to try?
>
>
> On Tue, Mar 3, 2009 at 2:04 AM, John Smith <[email protected]> wrote:
>
>> I hate replying to myself but I also noticed that this problem is only in
>> the case where the vector is storing an object not a pointer to an object.
>> (Which is why I think I'm hitting a copy constructor at some point instead
>> of having it pass by reference)
>>
>> If I was to modify the container to be std::vector<ContainedObject *>
>> vec;, and modify the test code to be:
>> ContainerObject cont;
>> ContainedObject* Obj = new ContainedObject;
>>
>> Obj->value = 10;
>>
>> cont.push_back(Obj);
>>
>> Then when I come out of the call_function Obj has the expected value of
>> 5.
>>
>> Anyone have other ideas/thoughts?
>>
>>
>> On Tue, Mar 3, 2009 at 1:57 AM, John Smith <[email protected]> wrote:
>>
>>> I don't believe so, changing that to be : gave the following errors:
>>> print(cont:containervalue)
>>> function arguments expected near ')' for that line
>>>
>>> for things in cont:vec
>>> gave the error:
>>>  function arguments expected near 'do'
>>>
>>> My understanding of the : notation was that it was a shorthand of:
>>> x:y is equivilant to x.y(x)
>>>
>>> Therefore, trying:
>>> for things in cont:vec()
>>>
>>> gave a luabind exception of 'No such operator defined'
>>>
>>>
>>>
>>> On Tue, Mar 3, 2009 at 1:26 AM, James Porter <[email protected]>wrote:
>>>
>>>> John Smith wrote:
>>>> > Lua code:
>>>> > function LuaFunction( cont )
>>>> >     print (cont.containervalue)
>>>> >     cont.containervalue = 30
>>>> >     for things in cont.vec
>>>> >     do
>>>> >         print (things.value)
>>>> >         things.vlaue = 5
>>>> >     end
>>>> > end
>>>>
>>>> It looks like you're using the wrong syntax for getting at your members.
>>>> In Lua, "." is similar to "::" in C++, while ":" in Lua is similar to
>>>> "." in C++. You want cont:containervalue, cont:vec, and so on. The
>>>> former is working because you're defining a new static variable,
>>>> essentially.
>>>>
>>>> - Jim
>>>>
>>>>
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>>>
>>
>
>
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> -Strategies to boost innovation and cut costs with open source
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