Re: Would this be a valid use of inheritance?

From:

Joe Greer <jgreer@doubletake.com>

Newsgroups:

comp.lang.c++

Date:

Tue, 2 Sep 2008 18:52:00 +0000 (UTC)

Message-ID:

<Xns9B0D973B52E44jgreerdoubletakecom@85.214.90.236>

Juha Nieminen <nospam@thanks.invalid> wrote in
news:jVitk.247$bi6.65@read4.inet.fi:

  So I was thinking, would this be a valid way of circumventing the
  problem?

//---------------------------------------------------------------------
template<typename Data_t, typename Alloc_t = std::allocator<Data_t> >
class SmartPtr: private Alloc_t
{
    Data_t* data;
    // And whatever is needed for reference counting, if anything

    void decRefCount()
    {
        // Decrement the reference count, and then:
        if(<refcount is 0>)
        {
            destroy(data);
            deallocate(data, 1);
        }
    }

public:
    SmartPtr(Data_t* d, const Alloc_t& a):
        Alloc_t(a), data(d)
    {
        // init refcount, or whatever
    }

    // Plus the other necessary functions.
};
//---------------------------------------------------------------------

  I know this is badly misusing inheritance for an ugly hack, but now
  an
empty allocator class will not increase the size of the smart pointer,
but the smart pointer can still be told which allocator to use to
destroy the object.

  Can you think of any reason why this would be a very bad idea?

I think that the same reason that smart_ptr<> is the way it is in the
standard is a good enough reason not to do this. Basically, since the
allocator is now part of the smart pointer type, it can't interact with
functions written to accept a smart pointer of type Data_t with a different
allocator. This can become a real pain in the backside for large projects.

joe