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

Subject: Re: [boost] [interest] rich-typed smart pointers
From: Larry Evans (cppljevans_at_[hidden])
Date: 2013-10-06 00:14:05

On 10/05/13 20:14, Larry Evans wrote:
> 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]
>
Coded it but it failed to compile because
owner_ptr<shape> could not assign a nullptr to 
owner_ptr<circle>::pointer because (as you mentioned)
owner_ptr<shape> is not a fried of owner_ptr<circle>.

Sorry for noise.

-regards,
Larry