#include <stdio.h>

template<class T>
struct A
{ };

struct B
{ };

template<class U, class T>
A<U> f(T t)
{
  printf("1\n");
  return A<U>();
}

template<class T>
A<B> f(T t)
// Error: 'f' previously declared as something else
// It was declared as: A<U>C func(T)
// It is now declared: A<B>C func(T)
{
  printf("2\n");
  return A<B>();
}

int main()
{
  f(0);
  // Error: ambiguous reference to symbol
  f<int>(0);
  // Error: ambiguous reference to symbol

  return 0;
}


Extracted from Boost.Bind (to get adaptable function objects working).

gcc-3.0 chooses the second function for "f(0)" and the first one for
"f<int>(0)" and I guess that's what Boost.Bind expects.


bye, Christof

-- 
http://cmeerw.org                                 JID: cmeerw@jabber.at mailto cmeerw at web.de

...and what have you contributed to the Net?

I've fixed the first issue, 'Error: 'f' previously declared as something else'. But I think the other two should be ambiguous, I cannot find a rule that gives the results you are seeing from gcc-3.0.


"Christof Meerwald" <cmeerw@web.de> wrote in message news:au7ab9$67p$1@digitaldaemon.com...
> #include <stdio.h>
>
> template<class T>
> struct A
> { };
>
> struct B
> { };
>
> template<class U, class T>
> A<U> f(T t)
> {
>   printf("1\n");
>   return A<U>();
> }
>
> template<class T>
> A<B> f(T t)
> // Error: 'f' previously declared as something else
> // It was declared as: A<U>C func(T)
> // It is now declared: A<B>C func(T)
> {
>   printf("2\n");
>   return A<B>();
> }
>
> int main()
> {
>   f(0);
>   // Error: ambiguous reference to symbol
>   f<int>(0);
>   // Error: ambiguous reference to symbol
>
>   return 0;
> }
>
>
> Extracted from Boost.Bind (to get adaptable function objects working).
>
> gcc-3.0 chooses the second function for "f(0)" and the first one for
> "f<int>(0)" and I guess that's what Boost.Bind expects.
>
>
> bye, Christof
>
> --
> http://cmeerw.org                                 JID: cmeerw@jabber.at mailto cmeerw at web.de
>
> ...and what have you contributed to the Net?

On Tue, 31 Dec 2002 14:18:54 -0800, Walter wrote:
> I've fixed the first issue, 'Error: 'f' previously declared as something
> else'. But I think the other two should be ambiguous, I cannot find a rule
> that gives the results you are seeing from gcc-3.0.
> "Christof Meerwald" <cmeerw@web.de> wrote in message
> news:au7ab9$67p$1@digitaldaemon.com...
>> #include <stdio.h>
>>
>> template<class T>
>> struct A
>> { };
>>
>> struct B
>> { };
>>
>> template<class U, class T>
>> A<U> f(T t)
>> {
>>   printf("1\n");
>>   return A<U>();
>> }
>>
>> template<class T>
>> A<B> f(T t)
>> {
>>   printf("2\n");
>>   return A<B>();
>> }
>>
>> int main()
>> {
>>   f(0);
>>   // Error: ambiguous reference to symbol

See 14.8.3 Overload resolution [temp.over]

"If, for a given function template, argument deduction fails, no such function is added to the set of candidate functions for that template."

And argument deduction should fail for "template<class U, class T> A<U> f(T
t)" (because U can't be deduced), therefore it should not be added to the
set of candidate functions leaving "template<class T> A<B> f(T t)" as the
only possible candidate.


>>   f<int>(0);
>>   // Error: ambiguous reference to symbol

See 14.5.5.2 Partial ordering of function templates [temp.func.order], paragraphes 3 and 4.

"template<class U, class T> A<U> f(T t)" is at least as specialized as
"template<class T> A<B> f(T t)".

But, "template<class T> A<B> f(T t)" is not at least as specialized as
"template<class U, class T> A<U> f(T t)" (argument deduction fails because U
can't be deduced from the function parameter list)

Thus "template<class U, class T> A<U> f(T t)" is more specialized than
"template<class T> A<B> f(T t)" and should therefore be selected.


That's my interpretation of the standard...


bye, Christof

PS: Happy New Year! :-)

-- 
http://cmeerw.org                                 JID: cmeerw@jabber.at mailto cmeerw at web.de

...and what have you contributed to the Net?

All right. That does make some sense. I'll check it out. -Walter

"Christof Meerwald" <cmeerw@web.de> wrote in message news:autg6u$1e2h$1@digitaldaemon.com...
> On Tue, 31 Dec 2002 14:18:54 -0800, Walter wrote:
> > I've fixed the first issue, 'Error: 'f' previously declared as something else'. But I think the other two should be ambiguous, I cannot find a
rule
> > that gives the results you are seeing from gcc-3.0. "Christof Meerwald" <cmeerw@web.de> wrote in message news:au7ab9$67p$1@digitaldaemon.com...
> >> #include <stdio.h>
> >>
> >> template<class T>
> >> struct A
> >> { };
> >>
> >> struct B
> >> { };
> >>
> >> template<class U, class T>
> >> A<U> f(T t)
> >> {
> >>   printf("1\n");
> >>   return A<U>();
> >> }
> >>
> >> template<class T>
> >> A<B> f(T t)
> >> {
> >>   printf("2\n");
> >>   return A<B>();
> >> }
> >>
> >> int main()
> >> {
> >>   f(0);
> >>   // Error: ambiguous reference to symbol
>
> See 14.8.3 Overload resolution [temp.over]
>
> "If, for a given function template, argument deduction fails, no such function is added to the set of candidate functions for that template."
>
> And argument deduction should fail for "template<class U, class T> A<U>
f(T
> t)" (because U can't be deduced), therefore it should not be added to the
> set of candidate functions leaving "template<class T> A<B> f(T t)" as the
> only possible candidate.
>
>
> >>   f<int>(0);
> >>   // Error: ambiguous reference to symbol
>
> See 14.5.5.2 Partial ordering of function templates [temp.func.order], paragraphes 3 and 4.
>
> "template<class U, class T> A<U> f(T t)" is at least as specialized as
> "template<class T> A<B> f(T t)".
>
> But, "template<class T> A<B> f(T t)" is not at least as specialized as
> "template<class U, class T> A<U> f(T t)" (argument deduction fails because
U
> can't be deduced from the function parameter list)
>
> Thus "template<class U, class T> A<U> f(T t)" is more specialized than
> "template<class T> A<B> f(T t)" and should therefore be selected.
>
>
> That's my interpretation of the standard...
>
>
> bye, Christof
>
> PS: Happy New Year! :-)
>
> --
> http://cmeerw.org                                 JID: cmeerw@jabber.at mailto cmeerw at web.de
>
> ...and what have you contributed to the Net?