Re: [Boost-bugs] [Boost C++ Libraries] #3645: iterator_facade does not work in presence of ::implicit_cast

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #3645: iterator_facade does not work in presence of ::implicit_cast
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2009-11-19 18:04:42

#3645: iterator_facade does not work in presence of ::implicit_cast
-------------------------------+--------------------------------------------
 Reporter:  romanp@…           |       Owner:         
     Type:  Bugs               |      Status:  new    
Milestone:  Boost 1.42.0       |   Component:  None   
  Version:  Boost 1.41.0       |    Severity:  Problem
 Keywords:  iterator_facade    |  
-------------------------------+--------------------------------------------

Comment(by romanp@…):

 The compiler is right to complain about ambiguity.

 14.8.1 - Explicit template argument specification [temp.arg.explicit]

 -6- [Note: For simple function names, argument dependent lookup
 (basic.lookup.koenig) applies even when the function name is not visible
 within the scope of the call. This is because the call still has the
 syntactic form of a function call (basic.lookup.unqual). But when a
 function template with explicit template arguments is used, the call does
 not have the correct syntactic form unless there is a function template
 with that name visible at the point of the call. If no such name is
 visible, the call is not syntactically well-formed and argument-dependent
 lookup does not apply. If some such name is visible, argument dependent
 lookup applies and additional function templates may be found in other
 namespaces. [Example:

 namespace A {
        struct B { };
        template<int X> void f(B);
 }
 namespace C {
        template<class T> void f(T t);
 }
 void g(A::B b) {
        f<3>(b);                //  ill-formed: not a function call
        A::f<3>(b);             //  well-formed
        C::f<3>(b);             //  ill-formed; argument dependent lookup
                                //  only applies to unqualified names
        using C::f;
        f<3>(b);                //  well-formed because  C::f  is visible;
 then
                                //   A::f  is found by argument dependent
 lookup
 }

 --- end example]
 --- end note]

 Which means that iterator_facade has unintended point of extension (ADL
 enabled call).

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/3645#comment:2>
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