Re: EBCO - why does it require inheritance?

From:

Joe Greer <jgreer@doubletake.com>

Newsgroups:

comp.lang.c++

Date:

Wed, 22 Aug 2007 14:17:34 +0200 (CEST)

Message-ID:

<Xns9994545BFAC59jgreerdoubletakecom@194.177.96.78>

Chris Fairles <chris.fairles@gmail.com> wrote in
news:1187716997.858600.229750@g4g2000hsf.googlegroups.com:

This all came about while implementing unique_ptr for c++0x.

template <class _Tp>
struct default_delete : public unary_function<_Tp*,void> {
  default_delete() {}
  template <class _Up> default_delete(const default_delete<_Up>&) {}
  void operator()(_Tp* __ptr) const {
    static_assert(sizeof(_Tp) > 0, "can't delete pointer to incomplete
type");
    delete __ptr;
  }
};

template <class _Tp, class _Tp_Deleter = default_delete<_Tp>>
class unique_ptr {
/* ... */

  _Tp* __ptr;
  _Tp_Deleter __deleter;
};

Given the nature of your deleter's, you can either make the method static like:

template <class _Tp>
struct default_delete : public unary_function<_Tp*,void> {
   default_delete() {} template <class _Up> default_delete(const default_delete
_Up>&) {}
   static void delete(_Tp* __ptr) const {
     static_assert(sizeof(_Tp) > 0, "can't delete pointer to incomplete
type");
     delete __ptr;
   }
};

template <class _Tp, class _Tp_Deleter = default_delete<_Tp>>
class unique_ptr {
/* ... */

   _Tp* __ptr;
   ~unique_ptr() { _Tp_Deleter::delete(__ptr); }
};

or you can instatiate it when you need it rather than at construction time.

template <class _Tp, class _Tp_Deleter = default_delete<_Tp>>
class unique_ptr {
/* ... */

   _Tp* __ptr;
   ~unique_ptr() { _Tp_Deleter()(__ptr); }
};

Just some thoughts,
joe