Re: [Boost-users] Re: [Foreach]TroubleiteratingoverBoost.MultiIndexcontainers

4 Mar 2005

      Arkadiy Vertleyb wrote:
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"Thorsten Ottosen"  wrote
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"Arkadiy Vertleyb"  wrote
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"Thorsten Ottosen"  wrote
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"Arkadiy Vertleyb"  wrote in message
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I don't get this. Surely one of the functions would be a better
match than the others and hence called.
How is
namespace MyNamespace
{
   template<class T> end(const T&);
}
is better match than
namespace YourNamespace
{
   template<class T> end(const T&);
}
?
And now:
MyNamespace::FooYourNamespace::Bar obj;
end(obj); // ?????
Why would any function but the primary template be taking
a const T& param, that is, why don't your
YourNamespace::end() refer to some class in YourNamespace?
Because one may have many unrelated templates that support the same
concept. Consider your range library.  What if one wants to write
end() that is good for any std container?
The above is not a proper use of ADL. It's similar to

namespace MyNamespace
{
        template<class T> T operator-(const T&);
}

namespace YourNamespace
{
    template<class T> T operator-(const T&);
}

This would obviously break -x, when x has both MyNamespace and YourNamespace 
as associated namespaces. Not only that; the definition in MyNamespace can 
break -x by itself, when x has an unary operator- that is reachable via a 
conversion. Yet few people qualify their operators or provide class 
templates as customization points. A disaster waiting to happen, surely.

Re: [Boost-users] Re: [Foreach]TroubleiteratingoverBoost.MultiIndexcontainers

Peter Dimov