Re: [boost] [interest] rich-typed smart pointers

Subject: Re: [boost] [interest] rich-typed smart pointers
From: Larry Evans (cppljevans_at_[hidden])
Date: 2013-10-05 21:14:38

On 10/05/13 16:26, Julian Gonggrijp wrote:
> Larry Evans wrote:
>
>>> https://github.com/jgonggrijp/rich-typed-pointers
>> [snip]
>> If there were a templated owned_ptr CTOR:
>>
>>     template<typename Derived>
>>     owner_ptr (owner_ptr<Derived> && source) : pointer(source.pointer) {
>>         source.pointer = nullptr;
>>     }
>>
>> wouldn't that eliminate the need for the make_dynamic templated function?
>>
>> Just wondering.  I haven't tried it, but I'd guess it would work because
>> the ownd_ptr<Derived> could be constructed with the:
>>
>>   make<Derived>(t1,t2,...tn)
>>
>> and then the templated owned_ptr CTOR would then convert that to the
>> base class?
>
> I agree this would be great, but unfortunately it appears it can't be done.
> owner_ptr<Derived> would have to friend-declare owner_ptr<Base>,
I don't see why.  AFAICT, you'd require *fewer* friend declarations, not 
more( you wouldn't need the:

     template <class U1, class U2, class ... Us>
     friend owner_ptr<U1> make_dynamic (Us&& ...);

the only friend needed would the existing:

     template <class U, class ... Us>
     friend owner_ptr<U> make (Us&& ...);

that's because the proposed templated constructor would have the same
access as the existing:

     owner_ptr (owner_ptr && source);

CTOR, i.e. public.  IOW, with the proposed templated CTOR, the
following example code creating an owner_ptr<Base> should work,
AFAICT:

     owner_ptr<Base>
   owner_baee
     ( make<Derived>
       ( DerivedInit0()
       , DerivedInit1()
       .
       .
       . DerivedInitN()
       )
     );

Where DeriveInit0, DerivedInit1, ... DerivedInitN
are the types of the args to the CTOR for Derived.

Is there some reason why the above example code would
*not* compile, given then proposed templated CTOR?
[snip]

-regards,
Larry