[boost] Re: Customization via Overloading in Namespace

From: David Abrahams (dave_at_[hidden])
Date: 2004-02-20 17:33:19

Brian McNamara <lorgon_at_[hidden]> writes:

> On Fri, Feb 20, 2004 at 04:03:57PM -0500, David Abrahams wrote:
>> Simple: specializations that follow the point of instantiation aren't
>> considered.  This program exits with an error:
>> 
>>   template <class T>
>>   int f(T) { return 1; }
>> 
>>   int main()  { return ::f(0); }
>> 
>>   template <> int f(int) { return 0; }
>
> Aha; this is part of what I was missing.  
> This clears most of it up for me.
>
> One last question, and then I think I'm done.  In my example:
>
>    namespace lib {
>       template <class T> void f(T) { /* print "bar" */ }
>       template <class T> void g(T x) { lib::f(x); }     // (1)
>    }
>
>    namespace user {
>       struct MyClass {};
>    }
>    namespace lib {
>       template <> void f( user::MyClass ) { /* print "foo" */ }
>    }
>
>    int main() {
>       user::MyClass m;
>       lib::g(m);                                        // (2)       
>    }
>
> What is printed?

foo

> (I think this question comes down to whether or not (1) or (2) is the
>  "point of instantiation" of f(), yes?)

Yeah; if you change g so it callse lib::f(0) it prints bar.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com