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

From: Anthony Williams (anthony_w.geo_at_[hidden])
Date: 2006-04-07 12:57:17

Vladislav Lazarenko <snail_at_[hidden]> writes:

> Martin Bonner wrote:
>> 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.

I proposed a similar thing on comp.std.c++ in 2001:

http://groups.google.com/group/comp.std.c++/browse_thread/thread/accd1f3f57dfed60/c19fc42712e15296?lnk=st&q=comp.std.c%2B%2B+final+Anthony+Williams&rnum=1#c19fc42712e15296

Unfortunately the declaration "friend typename T", is not legal. It might
happen to work on current releases of Microsoft compilers, but that's a bug in
the compiler.

Anthony
-- 
Anthony Williams
Software Developer
Just Software Solutions Ltd
http://www.justsoftwaresolutions.co.uk