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

Subject: Re: [boost] How to create a shallow copy without callingaconstructor?
From: Stefan Strasser (strasser_at_[hidden])
Date: 2010-01-04 03:46:18

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?

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.

>
> > 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.

>
> 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, 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

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.