[boost] Sealed C++ class.

7 Apr 2006

      Dear Boost community,
I thank you for such wonderful library, I can not even imagine
my life without Boost. Great work, team!

I propose to add the small but sometimes very useful class (like 
boost::noncopyable) I developed it in hope it will be useful and included into 
the best C++ framework in the world.

Note that I have tested this class only with:

1) Microsoft Visual C++ .NET   55537-640-4008961-18142
2) Microsoft Visual C++ .NET   69462-112-0617214-18401

But I think it won't be a problem to compile with gcc and so one.
And, surely, sorry if there is already such class in the Boost,
I did not found. If it is, please give me the link, I will take a look.

Please review and let me know what you think by replying to this message.
Thank you very much in advance.

//
// Copyright (c) 2006 Vladislav Lazarenko <snail@b2bits.com>
//
// Distributed under the Boost Software License, Version 1.0. (See
// accompanying file LICENSE_1_0.txt or copy at
// http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef BOOST_SEALED_HPP
#define BOOST_SEALED_HPP

// MS compatible compilers support #pragma once.
#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once
#endif

namespace boost
{
   // protection from unintended ADL
   namespace sealed_
   {
     template <typename T1, typename T2>
     class sealed_impl
     {
       friend typename T1;
       friend typename T2;

     private:
       sealed_impl() {}
       ~sealed_impl() {}
     };
   }

   /*!
       The sealed classes is used to prevent derivation from a class.
       An error occurs if a sealed class is specified as the base class of 
another class.
       A sealed class cannot also be an abstract class.
   */
   template <typename T>
   class sealed : virtual private sealed_::sealed_impl<sealed, T>
   {
   public:
     //! Constructor.
     sealed() {}

     //! Destructor.
     ~sealed() {}
   };

   // Usage example:
   /*
       class UniquePerson : public boost::sealed<UniquePerson>
       {
       public:
         UniquePerson() {}
         ~UniquePerson() {}
       };
   */
}

#endif