Re: [Boost-users] type_with_alignment

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2006-06-14 07:29:53

On Jun 14, 2006, at 4:56 AM, John Maddock wrote:

> Gottlob Frege wrote:
>>> if unknown_struct is an incomplete type (which is what I meant, and
>>> should have said), alignment_of doesn't compile.
>
> If the type is incomplete then you can't use aligned_storage  
> anyway, since
> you don't know how much storage you'll need!  Sorry but you've lost  
> me now.

There are applications such as boost::function where aligned storage  
for an unknown type is useful.  In boost::function's case, aligned  
storage could be used to implement the "short string optimization".   
The general pattern is:

class Container
{
private:
     const unsigned buf_size = ...;
     aligned_storage<buf_size>::type buffer;
public:
     template <class T>
        Container(const T& t) {/* might stick t into buffer instead  
of on heap, based on sizeof(T) */}
};

On Jun 14, 2006, at 6:55 AM, David Abrahams wrote:

> I think what the OP is looking for is called boost::shared_ptr ;-)

shared_ptr can't compete with this application performance-wise.

-Howard