Re: namespace and global function

From:

SG <s.gesemann@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Fri, 18 Nov 2011 01:00:33 -0800 (PST)

Message-ID:

<7eab36fd-ab4f-4d9c-a2e3-d2956fe81a74@p1g2000yqh.googlegroups.com>

On Nov 17, 11:09 pm, Jayden Shui wrote:

I have a global function to clone an object.

  template<class T>
  T* Clone(T const& t)
  {
      return new T(t);
  }

and I have a class A in a namespace S which needs a specialized Clone
function

namespace S {

class A
{
    friend A* Clone(A const& a)
    {
        // do something special
        return new A(a);
    }
};
}

The clone function for S::A is introduced in the namespace S,
that is S::Clone.

That's not true. Clone is not injected into the namespace S. But it
can be found via ADL (argument dependent lookup).

It is not in the global scope. Is there any way to introduce
it in the global scope while still keeping the function body in the
namespace scope.

Why? Isn't ADL not enough for you? Just use "Clone" unqualified. If
you want to fall back on your global template you can do so with a
using declaration just to be safe

  namespace funky {

    template<class T>
    class indirect_value {
      T* ptr_;
    public:
      :::

      indirect_value(indirect_value const& x)
      : ptr_(0) {
        using ::Clone; // to avoid hiding issues with other, unrelated
Clone functions
        ptr_ = Clone(*x.ptr_); // ADL is applicable, falls back
on ::Clone
      }

      :::
    };

  }

You should understand how unqualified name lookup works.

Cheers!
SG