Re: [boost] [smart ptr] Any interest in copy-on-write pointer for C++11?

Subject: Re: [boost] [smart ptr] Any interest in copy-on-write pointer for C++11?
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2013-02-10 13:01:52

On 10/02/13 10:27, Vicente J. Botet Escriba wrote:

>> It seems to me that the copy of polymorphic object works only with the
>> help of the user and that the following should be mentioned as a
>> limitation
>>
>>             Base* ba = new Derived1;
>>             cow_ptr<Base> a( ba );
>>             cow_ptr<Base> c;
>>             c = a; // performs a shallow copy.
>>             c->doSomething(); // couldn't makes a deep copy of a as a
>> Derived1 class as the type has been lost.
>>                 // There is a slicing involved.
>>
>>
> If this is confirmed, I see it as a show-stopper, and the cloning
> strategy must be redefined.

This is something that I already pointed out elsewhere on the thread.
To me the best approach is to make the class have a "virtual copy 
constructor" (a clone virtual member function counts as one), which is 
the only way to fix this issue.

I don't quite like the approach in N3339 because it couples allocation 
and copy construction.