Re: [Boost-users] Serialization with pointer to const object

Subject: Re: [Boost-users] Serialization with pointer to const object
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2009-07-24 15:24:24

IMO even after the serialization library dereferences the
pointer-to-const, it should const_cast it to serialize the object,
because in the typical case the object is mutable. For example, if you
have:

int const * p=new int(42);

the object p points to is mutable and const_cast is well defined.
You'd have to do:

int const * p=new int const(42);

to get a const object, in which case const_cast would be undefined
behavior, but it seems that this would be extremely rare. Granted,
just looking at an int const * p you don't know if the object it
points to is mutable or not, but I think that const_cast is a rather
safe bet in this case and Soumen is correct to expect the
serialization of a pointer-to-const to "just work."

Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode

On Fri, Jul 24, 2009 at 1:10 PM, Robert Ramey<ramey_at_[hidden]> wrote:
> Hmmm - good point.  In the past I sort of made this decision in an ad-hoc
> way without thinking too much about it.
>
> Thinking about now.
>
> const * A m_a
>
> is a pointer to a const object. I would not expect the following to work
>
> ar << m_a
>
> I would not expect it to trap at the right level- but at the lower level
> after m_a
> is de-referenced to a const A & and THAT is serialized.
>
> I'm not sure where it's traping now though.
>
> Robert Ramey
>
> Emil Dotchevski wrote:
>> But in his case the object he is serializing (the pointer itself)
>> isn't const. In addition, in the typical use case the object the
>> pointer points to is also mutable. Shouldn't the const_cast be in
>> Boost Serialization?
>>
>> Emil Dotchevski
>> Reverge Studios, Inc.
>> http://www.revergestudios.com/reblog/index.php?n=ReCode
>>
>> On Fri, Jul 24, 2009 at 9:33 AM, Robert Ramey<ramey_at_[hidden]> wrote:
>>> Hmm - a const object is one that can't be changed once created. If
>>> you think about it, this conflicts with what serialization is. If in
>>> spite of this, you still want to do it, it is possible. Use
>>> const_cast. Also there information in the documentation regarding
>>> this.
>>>
>>> Robert Ramey
>>>
>>> Soumen wrote:
>>>> Hi,
>>>>
>>>> I'm using gcc 4.2.2 and boost 1.35. If I try to serialize pointer to
>>>> some const objects, I'm getting compilation problem. Is there any
>>>> limitation? Or I need to do certain things differently? I couldn't
>>>> figured any solution over net. If there already exist any topic
>>>> which points to solution, please point me to that. Otherwise, guide
>>>> me to resolve the problem at hand. I'm new to boost.
>>>>
>>>> Say, my data member in the class myClass is
>>>>
>>>> const myType *ptr;
>>>>
>>>> In the serialize() routine, I'm doing it in following way:
>>>>
>>>> template< class Archive >
>>>> void myClass::serialize(Archive &ar, const unsigned int version)
>>>> {
>>>> ar & ptr;
>>>>
>>>> // I've tried "ar & const_cast< myType* >(ptr)" and
>>>> // "ar & (myType *) ptr" as well - it didn't work
>>>>
>>>> /* serialize other members */
>>>>
>>>> }
>>>>
>>>> Regards,
>>>> - Soumen
>
>
>
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