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

6 Oct 2013

      On 10/05/13 23:14, Larry Evans wrote:
...
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 
     friend owner_ptr<U1> make_dynamic (Us&& ...);
the only friend needed would the existing:
template 
     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.
Googling:

   c++ templated friend

lead to:

   http://stackoverflow.com/questions/3292795/template-friend

which lead to the owner_ptr CTOR code:

     template<typename Derived>
     owner_ptr (owner_ptr<Derived>&& source) : pointer(source.pointer) {
         source.pointer = nullptr;
     }
     template <class Derived>
     friend class owner_ptr;

in rich_typed_ptr.hpp which resulted in successful compile and run
of the shapes.cpp example without using make_dynamic.

HTH.

-regards,
Larry