This code fails on 8.50.1n while it works with Comeau
and looks well formed.

It is triggered by the friend declaration.

-----------------------
template <class T>
struct addable2
{
  friend T operator +( T lhs, const T& rhs ) { return lhs += rhs; }
};


template<class T>
struct addable : addable2<T>
{
};

template <class T>
class point  : addable< point<T> >
{
};

int main()
{
  point<int> ppp;
  return 0;
}
----------------------------

This bug manifests itself when
<boost/operators.hpp> is used.

/Pavel

Thanks!

> -----------------------
> template <class T>
> struct addable2
> {
>  friend T operator +( T lhs, const T& rhs ) { return lhs += rhs; }
> };
>
>
> template<class T>
> struct addable : addable2<T>
> {
> };
>
> template <class T>
> class point  : addable< point<T> >
> {
> };
>
> int main()
> {
>  point<int> ppp;
>  return 0;
> }
> ----------------------------
>

I'd checked the code against 8.50.2 beta.

The previous version said something about unknown
size of a structure, the current error message is

a.cpp(4) : Error: undefined use of struct or union

/Pavel

Pavel Vozenilek wrote:
>> -----------------------
>> template <class T>
>> struct addable2
>> {
>>  friend T operator +( T lhs, const T& rhs ) { return lhs += rhs; }
>> };
>>
>>
>> template<class T>
>> struct addable : addable2<T>
>> {
>> };
>>
>> template <class T>
>> class point  : addable< point<T> >
>> {
>> };
>>
>> int main()
>> {
>>  point<int> ppp;
>>  return 0;
>> }
>> ----------------------------
>>
> 
> I'd checked the code against 8.50.2 beta.
> 
> The previous version said something about unknown
> size of a structure, the current error message is
> 
> a.cpp(4) : Error: undefined use of struct or union

That's because there's no += defined for point.

"Walter Bright"  wrote
> Pavel Vozenilek wrote:
>>> -----------------------
>>> template <class T>
>>> struct addable2
>>> {
>>>  friend T operator +( T lhs, const T& rhs ) { return lhs += rhs; }
>>> };
>>>
>>>
>>> template<class T>
>>> struct addable : addable2<T>
>>> {
>>> };
>>>
>>> template <class T>
>>> class point  : addable< point<T> >
>>> {
>>> };
>>>
>>> int main()
>>> {
>>>  point<int> ppp;
>>>  return 0;
>>> }
>>> ----------------------------
>>>
>>
>> I'd checked the code against 8.50.2 beta.
>>
>> The previous version said something about unknown
>> size of a structure, the current error message is
>>
>> a.cpp(4) : Error: undefined use of struct or union
>
> That's because there's no += defined for point.
>


Hmm. The operator is not called so it may not matter
(opinion, I am no C++ lawyer).

Comeau does not complain, neither does GCC 3.4.5
and VC++ 2005 also compiles it w/o problems.

/Pavel

"Pavel Vozenilek" wrote
>
> "Walter Bright"  wrote
>> Pavel Vozenilek wrote:
>>>> -----------------------
>>>> template <class T>
>>>> struct addable2
>>>> {
>>>>  friend T operator +( T lhs, const T& rhs ) { return lhs += rhs; }
>>>> };
>>>>
>>>>
>>>> template<class T>
>>>> struct addable : addable2<T>
>>>> {
>>>> };
>>>>
>>>> template <class T>
>>>> class point  : addable< point<T> >
>>>> {
>>>> };
>>>>
>>>> int main()
>>>> {
>>>>  point<int> ppp;
>>>>  return 0;
>>>> }
>>>> ----------------------------
>>>>
>>>
>>> I'd checked the code against 8.50.2 beta.
>>>
>>> The previous version said something about unknown
>>> size of a structure, the current error message is
>>>
>>> a.cpp(4) : Error: undefined use of struct or union
>>
>> That's because there's no += defined for point.
>>
>
>
> Hmm. The operator is not called so it may not matter
> (opinion, I am no C++ lawyer).
>
> Comeau does not complain, neither does GCC 3.4.5
> and VC++ 2005 also compiles it w/o problems.
>
> /Pavel
>

Borland C++ 6.4 compiles the snippet as well.
/Pavel

Here's another snippet showing the problem (extracted from <boost/operators.hpp>):

---------a.cpp---------------
template <class T>
struct decrementable
{
  friend T operator--(decrementable& x, int)
  {
    decrementable_type nrv(x);
    --x;
    return nrv;
  }
private:
  typedef T decrementable_type;
};



int main( int , char * [] )
{
  decrementable<int> a;
  return 0;
}
---------------------

Comeau does compile it.

/Pavel

Pavel Vozenilek wrote:
> Hmm. The operator is not called so it may not matter
> (opinion, I am no C++ lawyer).
> 
> Comeau does not complain, neither does GCC 3.4.5
> and VC++ 2005 also compiles it w/o problems.

Could you put a syntax error in the function and see if it complains?

"Walter Bright" wrote:

> Pavel Vozenilek wrote:
>> Hmm. The operator is not called so it may not matter
>> (opinion, I am no C++ lawyer).
>>
>> Comeau does not complain, neither does GCC 3.4.5
>> and VC++ 2005 also compiles it w/o problems.
>
> Could you put a syntax error in the function and see if it complains?
>


With VC++ 2005 syntax error within the unused function doesn't matter.

GCC 3.4.5 fails with error about the syntax,
Comeau also fails with the syntax.


I read somewhere that unused members
can be optionally syntactically checked but not semantically.


A search on newsgroups seems to confirm this:

Fergus Henderson: [T]he implementation _must not_ check
[unused template member] (other than
syntax checking)." (post from year 1995)

http://groups.google.com/group/comp.std.c++/msg/0cb95f20593b7777

/Pavel

Pavel Vozenilek wrote:
> I read somewhere that unused members
> can be optionally syntactically checked but not semantically.
> 
> 
> A search on newsgroups seems to confirm this:
> 
> Fergus Henderson: [T]he implementation _must not_ check
> [unused template member] (other than
> syntax checking)." (post from year 1995)
> 
> http://groups.google.com/group/comp.std.c++/msg/0cb95f20593b7777

But a friend is not a member.