🚀 go-pugleaf

In article <48bdf0$cou@panix.com>,
ajb@panix.com (Atman Binstock) wrote:

|> Can a namespace be a template argument?
|> ex:
|> template<namespace N> void f()
|> {
|> 	N::Fast_real r;
|> 	//...

No. We discussed this a fair bit in the committee. I was basically in
favour but there are some complications based on the fact that you can
extend a namespace and this makes it harder to specify the lookup rules for
name binding in templates. You can work around it with a struct with only
static members:

  struct N {
    static void f();
    typedef int T;
  };
  template<typename FakeNamespace> class A {
    typename FakeNamespace::T i;
    void g() { FakeNamespace::f(); }
  };
  A<N> an;

[note: typename is required in the declaration of A::i]

Perhaps C++ v2.0 will get everything templatised (we don't have template
variables, typedefs or namespaces but they can all, to some extent, be
synthesised today).

|> What is name injection??

You don't want to know, honest! :-)

  template<typename T> class X {
    friend void f();
  };
  // f not visible here
  X<int> xi; // cause friend declaration to be injected
  // f is now visible and can be called

This is different to non-template classes where friend declarations are
'injected' immediately:

  class C {
    friend void f();
  };
  // f _is_ visible here

But there's all sorts of nasty problems with name injection (I could write
a book :-) and we're trying to figure out how to achieve the desirable
parts without the undesirable parts.

Sean A. Corfield
Object Consultancy Services
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