Re: c++/9053: g++ confused about ambiguity of overloaded function templates

Re: c++/9053: g++ confused about ambiguity of overloaded function templates

[nathan]

Synopsis: g++ confused about ambiguity of overloaded function templates

State-Changed-From-To: analyzed->closed
State-Changed-By: nathan
State-Changed-When: Tue Dec 24 14:11:07 2002
State-Changed-Why:
    2002-12-24  Nathan Sidwell  <nathan@codesourcery.com>
    
    	PR c++/9053
    	* decl.c (duplicate_decls): Templates may be disambiguated by
    	return type.
    	
    	PR c++/8702
    	* decl2.c (check_classfn): Use lookup_fnfield_1. List all
    	conversion operators on failure.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9053

Re: c++/9053: g++ confused about ambiguity of overloaded function templates

[nathan]

Synopsis: g++ confused about ambiguity of overloaded function templates

Responsible-Changed-From-To: unassigned->nathan
Responsible-Changed-By: nathan
Responsible-Changed-When: Tue Dec 24 11:25:21 2002
Responsible-Changed-Why:
    strange,I could've sworn I fixed this.
State-Changed-From-To: open->analyzed
State-Changed-By: nathan
State-Changed-When: Tue Dec 24 11:25:21 2002
State-Changed-Why:
    confirmed.

http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&pr=9053

c++/9053: g++ confused about ambiguity of overloaded function templates

[martin]

>Number:         9053
>Category:       c++
>Synopsis:       g++ confused about ambiguity of overloaded function templates
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    unassigned
>State:          open
>Class:          rejects-legal
>Submitter-Id:   net
>Arrival-Date:   Tue Dec 24 10:36:00 PST 2002
>Closed-Date:
>Last-Modified:
>Originator:     Martin Buchholz
>Release:        g++ 3.2.1
>Organization:
>Environment:
Linux x86
>Description:
g++ must consider whether return types
of function templates lead to substitution failure
before giving an ambiguity error.  Considering only
arguments is insufficient.

These two function templates

template <class T> typename bar<T>::type foo (T);
template <class T> typename qux<T>::type foo (T);

look ambiguous, but may not be if, when instantiated
with a particular type, one of bar<T> or qux<T>
leads to substitution failure.

Easier to give an example than explain...

The code below compiles under icc and Comeau C++,
but not g++.

(Also: g++ gives ambiguity errors even if foo is never
instantiated, which is probably wrong.)

g++ gives:
ambiguous-template-bug2.cc:10: new declaration `template<class T> qux::type 
   foo(T)'
ambiguous-template-bug2.cc:7: ambiguates old declaration `template<class T> 
   bar::type foo(T)'


source code:

template <typename T> class bar;
template <> struct bar<const char*> { typedef void type; };
template <typename T> class qux;
template <> struct qux<int> { typedef void type; };

template <typename T>
typename bar<T>::type foo (T t) { }

template <typename T>
typename qux<T>::type foo (T t) { }


int
main (int argc, char *argv[])
{
  foo ("foo");
  foo (7);
}
>How-To-Repeat:
Compile source code with g++
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: