Re: Why koenig lookup?

From:
kwikius <andy@servocomm.freeserve.co.uk>
Newsgroups:
comp.lang.c++
Date:
Mon, 11 Aug 2008 01:09:48 +0100
Message-ID:
<489f833b$1_3@mk-nntp-2.news.uk.tiscali.com>
Jerry Coffin wrote:

In article <2a0f00c3-10cd-4b64-8203-57c5e681b565
@k13g2000hse.googlegroups.com>, james.kanze@gmail.com says...

[ ... ]

But doesn't use sin in a dependent context in a dependent
context in the template. I was thinking of the classical case,
where the operator<< for std::vector<int> defined in global
namespace doesn't get found when it is used in
std::ostream_iterator. Curiously, I can't reproduce the
symptomes in a simple example, but I've definitely had the
problem myself, and people post it here from time to time.


Here's a fairly simple example:

#include <map>
#include <string>
#include <iostream>
#include <algorithm>

typedef std::map<std::string, int> s_int;

//namespace std {

std::ostream &operator<<(std::ostream &os, s_int::value_type const &v)
{
    return os << v.first << ": " << v.second;
}

//}

int main() {
    s_int m;

    m["a"] = 123;
    m["b"] = 345;

    std::copy(m.begin(), m.end(),
        std::ostream_iterator<s_int::value_type>(std::cout, "\n"));

    return 0;
}

As it stands right now, it won't compile -- but remove the two comment
delimiters so operator<< is in namespace std, and it compiles and works
just fine.


Lemme guess. operator<<(std::ostream&, int ) is ***NOT*** in global
namespace Right? .. Which is the whole point!

I'm with Alf Steinbach on this one....

regards
Andy Little

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