Re: [boost] is_virtual_base_of ?

Subject: Re: [boost] is_virtual_base_of ?
From: Daniel Frey (d.frey_at_[hidden])
Date: 2009-03-08 06:31:22

On 08.03.2009, at 11:02, John Maddock wrote:

>> If not is there a way to make such a thing?
 > Can't think of a method off the top of my head, but Boosters are a  
clever lot so you never know....!

One can check if the size changes when creating another class:

template< typename D, typename B >
struct is_virtual_base_of
{
   struct X : D, virtual B {};
   enum { value = sizeof(X)==sizeof(D) };
};

template< typename T >
struct is_virtual_base_of< T, T >
{
   enum { value = false };
};

it triggers some warnings with GCC in my experiments when a base class  
is *not* virtual, but it seems to detect virtual bases just fine.  
Disclaimer: It's a start, nothing more. I have no idea how other  
compilers (even other compiler versions of GCC other than 4.3.2) will  
react on it, etc.

Regards, Daniel