Re: [boost] Sealed C++ class (error description)

From: Vladislav Lazarenko (snail_at_[hidden])
Date: 2006-04-07 12:36:31

Martin Bonner wrote:
> ----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.
> 
> 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;
> 	...
> 
> 7.1.5.3 p2 says "[Note: this implies that, within a class template with
> a template type-parameter T, the declaration friend class T; is
> ill-formed.]"
> 
> In other words, you can't do that :-(
> 

You are absolutely right. The only thing I am confused with is error 
description. The Boost is used not only by advanced developers, but by mid-level 
too. So when they will see such description it will be very difficult to find 
the real reason of error. Maybe I need just to put more comments in the header 
they will probably check.