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: 2013-02-09 21:04:06
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)?
> 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.
The conversion to bool should be explicit.
*explicit* operator bool() const noexcept;
Best,
Vicente