Re: [boost] Smart Pointer new/Forwarding Problem Solved (by Force)

From: Václav Veselý (vaclav.vesely_at_[hidden])
Date: 2006-03-29 01:05:13

David Abrahams wrote:
> I've developed some facilities that perhaps ought to be 
> developed into full-fledged libraries or components of 
> existing Boost libraries.
> This work centers around my long-standing threat to build a 
> library that could create smart pointers safely, without ever 
> exposing a raw pointer to the user.  For example,
> 
>   #include <memory>
>   #include <boost/shared_ptr.hpp>
>   #include "new.hpp"
> 
>   struct foo
>   { 
>     foo(int&, char const*, std::auto_ptr<int> const&);
>   };
> 
>   std::auto_ptr<int> x(new_<int>(3));
>   std::auto_ptr<foo> y(new_<foo>(*x, "hello, world", x));
>   boost::shared_ptr<foo> z(new_<foo>(*x, (char const*)"hello, 
> world", x));
> 
> To solve this problem correctly, it was necessary to address 
> "the forwarding problem"
> (http://std.dkuug.dk/jtc1/sc22/wg21/docs/papers/2002/n1385.htm
> ).  To that end, I developed some preprocessor macros that 
> one can use to generate the necessary overload sets.  Is 
> there interest in adopting any of this code (enclosed), and 
> if so, where should it go?

Yes, I'm interested.

IMHO maximum arity of about 5 isn't too restrictive. Except of this I would
like to have an alternative new_ with greater arity which use only const
reference forwarding. Non-const referrence parameters can be explicitly
wrapped with boost::ref.

I'm confused with syntax. new_<T> always creates auto_ptr<T>. How can I
create for example shared_ptr<T>?

How this is related to auto_overhead?

Regards,
Vaclav