Re: [boost] How to create a shallow copy without callingaconstructor?

Subject: Re: [boost] How to create a shallow copy without callingaconstructor?
From: Vicente Botet Escriba (vicente.botet_at_[hidden])
Date: 2010-01-04 04:12:03

Stefan Strasser-2 wrote:
> 
> Am Sunday 03 January 2010 18:59:24 schrieb vicente.botet:
>>
>> it can contain any non pointer type and pointers to transactional
>> objects,
>> but no pointer to non-transactional objects. The pointee transactional
>> objects do not need to be copied since the STM system track any
>> modification to them.
> 
> aren't you then really looking for a deep copy, excluding pointers to 
> transactional objects?
> 
yes, this could be said this way.

Stefan Strasser-2 wrote:
> 
> unfortunately there is no such concept of a "deep copy" in c++ either, so
> my 
> approach is to use Boost.Serialization for cloning objects (or a 
> user-supplied function).
> Using serialization you can decide on a case to case basis if the object 
> behind a pointer should be copied. (depending on if the type is 
> transactional, in your case).
> of course, that'd introduce the Serializable requirement and I don't know
> how 
> well that fits into your design.
> 
Non , serialization don't fits my requirements as I need to use the object
when deferred updating policy is used.

Stefan Strasser-2 wrote:
> 
> 
>>
>> > for the latter, you might want to make the decision if memcpy() can be
>> > used based on boost::serialization::is_bitwise_serializable.
>>
>> is_bitwise_serializable don't goes too far. it is equivalent to
>> is_artithmetic. But it can be specialized.
>>
>> I have find in Boost.TypeTraits this example
> 
> I don't think you can use type traits to make sure an object doesn't have 
> pointers (to non-transactional memory). I think you'll have to rely on the 
> user to provide that information.
> 
> 
I was talking of has_trivial_copy and has_trivial_assign.
Anyway, if the user provides a fusion sequence view of the structure, we can
decide if the structure has pointers to non-transactional objects.

Stefan Strasser-2 wrote:
> 
> 
>>
>> Of course, this force the user to define specific shallow copy semantics
>> operations, but IMO this will have some advantages. What do you think of
>> this approach?
> 
> how do you detect if a type provides this shallow copy constructor?
> as far as I know there is no way to statically detect that, 
> 
> 
I know that this cannot be detected. And the user will need to specialize
the trait.

Stefan Strasser-2 wrote:
> 
> 
> that's why I went 
> with inline friend functions, that can be found via ADL:
> https://svn.boost.org/svn/boost/sandbox/persistent/libs/persistent/doc/html/persistent/advanced.html#persistent.advanced.optmem
> 
Do you mean that I can request instead of the shallow copy constructor
request a make_shallow_copy?

        C* make_shallow_copy(C const &);

Stefan Strasser-2 wrote:
> 
> 
> this may be different in your case though because of the requirement to
> derive 
> from *_transaction_object, that could be used to detect which types ought
> to 
> provide a special copy constructor.
> 
> 

Sorry, I don't understand how the fact the type must derive from
base_transaction_object can help to define the has_shallow_copy_constructor.
Could you elaborate?

Thanks for your comments,
Vicente 
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