Re: std::auto_ptr and const correctness

From:

blargg.ei3@gishpuppy.com (blargg)

Newsgroups:

comp.lang.c++.moderated

Date:

Wed, 13 May 2009 10:11:08 CST

Message-ID:

<blargg.ei3-1305090515060001@192.168.1.4>

jens.muaddib@googlemail.com wrote:
[...]
I found a flaw in the

definition of std:.auto_ptr which breaks const-correctness

[...]

template<typename T>
class AutoPtr
{
public:
   explicit AutoPtr(T* ptr) : t(ptr) {}

   T* operator->() {return t;}
   T const* operator->() const {return t;}

   T* get() {return t;}
   T const* get() const {return t;}

private:
   T* t;
};

[...]

Additionally, the standards specifies std::auto_ptr to have the
following members:
// 20.4.5.2 members:
X& operator*() const throw();
X* operator>()
const throw();
X* get() const throw();
X* release() throw();
void reset(X* p =0) throw();

Is there any reason why the methods are specified const but return a
non-const pointer? I know that std::auto_ptr is deprecated, but this
looks as a serious flaw.

For the same reason

     int* get( int* const p ) { return p; }

works. An auto_ptr models a pointer; a const auto_ptr can't be modified,
but that says nothing of what it points to. Sounds like you want a smart
pointer which sort of models the object pointed to, so that a const smart
pointer to a non-const object can still only give you a pointer to const
object.

--
      [ See http://www.gotw.ca/resources/clcm.htm for info about ]
      [ comp.lang.c++.moderated. First time posters: Do this! ]