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From: Martin Bonner (martin.bonner_at_[hidden])
Date: 2006-04-07 11:35:27

----Original Message----
From: boost-bounces_at_[hidden]
[mailto:boost-bounces_at_[hidden]] On Behalf Of Sebastian Redl
Sent: 07 April 2006 16:14 To: boost_at_[hidden]
Subject: Re: [boost] Sealed C++ class.

> Vladislav Lazarenko wrote:
>> template <typename T>
>> class sealed : virtual private sealed_::sealed_impl<sealed, T>
> Interesting idea. Any particular reason why this inheritance is
> virtual?
> sealed_impl being a template should be rare to duplicate as a base,
> and
> having no data members or virtual functions, it should be irrelevant
> even if it was duplicated. On the other hand, you introduce the
> troubles
> that come with virtual inheritance.
> Sebastian Redl

If I write
        class Broken : public UniquePerson {};
Then the constructor of Broken has to invoke the constructor of
sealed_impl. However the constructor is private, so it can't. The
result is a compilation error.

The problem is the code:
     template <typename T1, typename T2>
     class sealed_impl
       friend typename T1;
       friend typename T2;
        ... p2 says "[Note: this implies that, within a class template with
a template type-parameter T, the declaration friend class T; is

In other words, you can't do that :-(

Martin Bonner
Pi Technology, Milton Hall, Ely Road, Milton, Cambridge, CB4 6WZ,
ENGLAND Tel: +44 (0)1223 203894

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