[boost] Re: Problem solved: EBO pessimization in smart_ptr not an issue anymore!

From: Gennadiy Rozental (rogeeff_at_[hidden])
Date: 2002-05-02 12:07:26

> ----- Original Message -----
> From: "Andrei Alexandrescu" <andrewalex_at_[hidden]>
>

Couple notes:

1. I like the idea. With only one exclusion: smart_ptr on singleton or
monotype object (in this case I can't skip constructor and destructor for
empty class). We should support the way for user to force inheritance.
2. It could be done without PC
3. I still feel that adding one level of indirection would be good.

So here I think it could look like:

template<typename Policies>
class basic_smart_ptr : public Policies
{
     typedef typename Policies::storage_policy storage_policy;
    ...
};

template<typename StoragePolicy,...>
struct simple_linear_policies_adaptor : StoragePolicy, OwnershipPolicy
{
    // typedefs

   // Constructors
};

template<bool first_is_empty,bool second_is_empty>
struct optional_parents_impl
{
     template<typename Mother,typename Father>
     struct are : Mother, Father
     {
       // Constructors
     };
};

template<>
struct optional_parents_impl<false,false>
...

template<>
struct optional_parents_impl<false,true>
...

template<>
struct optional_parents_impl<true,false>
...

template<typename Mother,typename Father>
struct optional_parents :
optional_parents_impl<is_empty<Mother>,is_empty<Father>
>::are<Mother,Father>
{
   // Constructors
};

template<typename StoragePolicy,...>
struct opt_linear_policies_adaptor : optional_parents<StoragePolicy,
optional_parents<OwnershipPolicy,...>>>>
{
    // typedefs

   // Constructors
};

template<typename Policy,typename Base>
struct vertical_adaptor : Policy, Base {}

template<typename StoragePolicy,...>
struct vertical_policies_adaptor : vertical_adaptor<StoragePolicy,
vertical_adaptor<OwnershipPolicy,...>>>>

template<typename StoragePolicy,...>
typedef basic_smart_ptr<opt_linear_policies_adaptor<StoragePolicy,...> >
smart_ptr;

Gennadiy.