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

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