[boost] Re: enabling ADL even with namespace qualification

13 Aug 2004


      Thorsten Ottosen wrote:
...
Maybe the following helps to create a more robust version of the idiom,
as it doesn't need 'using' at all:
[snip]
I think this won't work afterall.
Hm, good point. The only "solution" I could come up with is shown below, 
but I don't know how portable/robust it is.

#include <iostream>

namespace A
{
    // For this test, we assume sizeof(char) < sizeof(double)
    class internal { double dummy; };
    char operator,( const internal&, const internal& );

    template< typename T >
    internal f( const T& x )
    {
       if( sizeof( f(x),internal() ) == sizeof( char ) ) {
          // Non-ADL-implementation
          std::cout << 1 << std::endl;
       }
       else {
          // ADL-forwarder
          f( x );
       }
       return internal();
    }

    class C {};
}

namespace B
{
    class C {};

    void f( const C& )
    {
       std::cout << 2 << std::endl;
    }
}

int main()
{
    A::f( 42 );

    A::C c0;
    A::f( c0 );

    B::C c;
    A::f( c );
}

Regards, Daniel

-- 
Daniel Frey

aixigo AG - financial solutions & technology
Schloß-Rahe-Straße 15, 52072 Aachen, Germany
fon: +49 (0)241 936737-42, fax: +49 (0)241 936737-99
eMail: daniel.frey@aixigo.de, web: http://www.aixigo.de