[boost] Re: [pointer container] copyability

From: Pavel Chikulaev (pavel.chikulaev_at_[hidden])
Date: 2005-04-26 12:31:24

"David Abrahams" <dave_at_[hidden]> wrote in message 
news:uacnl8qsf.fsf_at_boost-consulting.com...
>
> I had this disagreement with Thorsten in Lillehammer (or was it
> Oxford?) but he was unimpressed with my arguments.

With mine too :(

> I was wondering what Boost as a whole would think:
>
> My Thesis: the library should support copying and assignment of
>  pointer containers using the usual copy/assignment syntax, rather
>  than only allowing a copy via a clone() function.

Agreed. But we should provide some traits class to support Clone, CloneMe
and so on. And some compile-time checking if user didn't provide any
clone functions.

> Rationale: Not being able to copy and assign pointer containers is an
>  arbitrary restriction that limits usefulness and expressivity.  The
>  argument Thorsten gives against copyability is that the elements
>  would have to be clone()d rather than copied, which is expensive
>  because there's a dynamic allocation per element.  I don't get it;

We might face with some problems with ptr_container's allocators
and the only solution is something to it is something like:

class Base
{
    size_t  size_of () const; // returns sizeof(*this);
    Base * placement_clone (void * address);
};

Or support only heap_clone_allocator... which might be undesirable
for some users.

P.S. What's your opinion about comparison operators? User is most
likely to going to have some polymorphic-related problems because
C++ doesn't provide virtual function specifier "must be overriden in
all derived classes".

--
Pavel Chikulaev