[boost] Re: boost::any feature request

From: Alexander Nasonov (alnsn-mycop_at_[hidden])
Date: 2003-03-25 10:27:18

Vladimir Prus wrote:
> Aha, that's what I was trying to say, but not very clearly. Yes, *this*
> will work. But... it means that if you do
> 
>    any<> a1;
>    any<fast_allocator> a2 = a1;
> Then value stored in a2 will be allocated using a1's allocator, not a2's.
> Once any is created with a specific allocator, all copies will use the
> same allocator, which is doubtful behaviour. In the example above, the
> "fast_allocator" parameter has no effect at all.
>
> Even if this behavior is desirable, you don't need to add template
> parameter  to 'any'.
I agree, there is no need for the template parameter for any.

> You can add template parameter to 'holder' only,
> and another constructor, which allows to specify allocator.
But then you can't make static_cast to holder<KnownType, UnknownAllocator> 
inside any_cast<KnownType>(a); May be wrap allocator specific stuff into 
separate interface?

There are two allocator types: (a) type specific ones like 
std::allocator<int> and (b) catch-all allocators.

Option (a) is probably better when you know the type:

  any<> a(1); // a uses new/delete
  any<> b(2, fast_allocator<int>());

I don't know whether to leave the original allocator or replace it with 
another one while making a copy:

   any<> c(a); // c uses new/delete
   any<> d(b); // d uses fast_allocator<int>?

-- 
Alexander Nasonov
Remove minus and all between minus and at from my e-mail for timely response