[boost] [RFC] Alternative any design

From: Pablo Aguilar (pablo.aguilar_at_[hidden])
Date: 2005-08-11 23:53:57

Hi,

First of all, thanks to everyone who's commented on the proposed any 
alternative.

Given that the alignment issue doesn't seem to be easy to solve, I'm 
thinking of giving up on trying to align correctly, and just skip the 
"in place storing of value" optimization when it might be an issue.

So I'm wondering, is the following a proper way to detect alignment 
problems?

<code>

typedef void*	any_buffer_base_type; // could be customized
int const	ANY_BUFFER_SIZE = sizeof(any_buffer_base_type);

union object_holder
{
   char  buffer[ANY_BUFFER_SIZE];
   void* pointer;

   any_buffer_base_type alignment_dummy_;
};
        
template<typename T>
struct optimize
{
   enum
   {
       T_size_    = sizeof(T)
     , base_size_ = sizeof(any_buffer_base_type)
     , size_ok_   = (T_size_ <= base_size_)

     , T_align_   = alignment_of<T>::value
     , base_align_= alignment_of<any_buffer_base_type>::value
     , align_ok_  = ((base_align_ % T_align_) == 0)

     , value      = size_ok_ && align_ok_
   };
};

</code>

I looked at Optional's alignment tecnique, and couldn't come up with how 
to use it, given that the stored type for any changes at runtime. If 
there's something I missed about this, any help would be welcome.

My current solution is to use the above shown code (assuming it works, 
of course!), and fall back on heap based storage when optimization is 
deemed not possible.

The 2nd question I had to ask is, how should any's alignment type be 
specified, with a configuration macro or through a template parameter?

I haven't posted an updated version, given that there's some issues 
(other than alignment) still requiring attention.

Thanks in advance for any help you might provide,

Pablo Aguilar