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: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-02-10 04:27:53

Le 10/02/13 03:04, Vicente J. Botet Escriba a écrit :
> Le 08/02/13 16:16, Ralph Tandetzky a écrit :
>> Hi,
>>
>> is there any interest in a copy-on-write pointer implementation? I 
>> wrote a cow_ptr<T> template class for C++11 which has the following 
>> use cases:
>>
>>
> As others I would prefer another name for the class. Could you compare 
> how you class relates to value_ptr as defined here 
> (file://localhost/Users/viboes/Downloads/n3339-1.pdf)?

I meant " N3339: A Preliminary Proposal for a Deep-Copying Smart 
Pointer" http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3339.pdf

>> 3. You can add cloning to a class hierarchy from the outside. With
>>             cow_ptr<Base> a( new Derived1 );
>>             cow_ptr<Base> b( new Derived2 );
>>             cow_ptr<Base> c;
>>             c = a; // performs a shallow copy.
>>             c->doSomething(); // makes a deep copy of a as a Derived1 
>> class.
>>                 // There is no slicing involved.
>> you copy Base objects polymorphically. The class Base can even be 
>> abstract here. It is only required that Derived1 and Derived2 be 
>> CopyConstructible.
>>
>
> 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.

I don't see any relational operators. Is this intentional?

It is worth adding interactions with nullptr_t?

What about a T* release() member function?

What about a reset(U*) member function ?

Best,
Vicente