Re: Why koenig lookup?

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Sun, 10 Aug 2008 18:45:46 +0200

Message-ID:

<peidnV2UeuxdhwLVnZ2dnUVZ_sudnZ2d@posted.comnet>

* James Kanze:

On Aug 10, 3:19 pm, "Alf P. Steinbach" <al...@start.no> wrote:

* James Kanze:

[...]

In addition:

    #include <BigDecimal.hh>

    int
    main()
    {
        using SomeNamespace::BigDecimal ;
        BigDecimal z1 ;
        BigDecimal z2 = sin( z1 ) ;
        // Do you really think it reasonable to have to write
        // SomeNamespace::sin here?
    }

I think this is a good point, that an overload of 'sin' should
not be introduced in a new namespace, but in the original
namespace, namely here the global one.

It doesn't work, because...

And of course, in a template, you don't really even have the
choice.

In a template, sin will be a dependent name, and will not be
looked up in the global namespace, only in the namespace where
BigDecimal was defined.

If that was true then it would just reinforce the point that ADL for named
routines has turned out to be too problematic, too many limiting corner cases.

However,

<code>
#include <iostream>

namespace james
{
     struct BigInt {};
}

double sin( james::BigInt ) { return 0; }

template< typename T >
void foo()
{
     sin( james::BigInt() );
}

namespace james
{
     template< typename T >
     void bar()
     {
         sin( BigInt() );
     }
}

int main()
{
     foo<char>();
     james::bar<char>();
}
</code>

is good standard C++.

So what you literally write, is incorrect, and argument void. But still there is
a good chance that you had some specific scenario in mind, that I don't at
present grok. And I'm interested in that, on its own, so please, elaborate. :-)

Cheers,

- Alf

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