Re: [boost] Adding polymorphic_value to boost

Subject: Re: [boost] Adding polymorphic_value to boost
From: Jonathan Coe (jonathanbcoe_at_[hidden])
Date: 2017-11-20 17:07:25

> On 20 Nov 2017, at 16:57, Peter Dimov via Boost <boost_at_[hidden]> wrote:
> 
> Jonathan Coe wrote:
> 
>> The pointer constructor is needed in migration paths from class heirarchies with a `Clone()` method. It also allows one to support objects coming from C_APIs.
> 
> Supporting
> 
>   X* create(...);
>   X* copy( X const* );
>   void destroy( X* );
> 
> is appropriate for a cloning pointer, but hasn't really much to do with polymorphic values.
> 
>   struct Shape
>   {
>       virtual ~Shape() = default;
>       Shape* clone() const = 0;
>       void draw() = 0;
>   };
> 
>   Shape* createCircle( int r );
> 
> is admittedly less clear-cut.
> 
> Looking at my old code, what I did was supply both a cloning pointer (U*) and a polymorphic value (U&&) types, the latter a simple wrapper over the former. 
> 

This was my original design too which was strongly opposed by LEWG. 

> _______________________________________________
> Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost