Using const references as local smart pointer?

From:
"Chris Thomasson" <cristom@comcast.net>
Newsgroups:
comp.lang.c++
Date:
Sun, 13 May 2007 12:43:46 -0700
Message-ID:
<Dc2dnSo2wOZE9NrbnZ2dnUVZ_rOqnZ2d@comcast.com>
I am fine-tuning some last minute things in my c++ allocator lib and was
thinking of ways to manage local references to system objects created with
factory functions. I started to tinker around with using const references to
represent a smart-pointer template that uses intrusive reference counting.
Anyway, here is a short little program that should clearly demonstrate what
I am messing around with:

_________________________
#include <cstdio>
#include <exception>

template<typename T>
class AutoRef {
  mutable T *m_State;

public:
  AutoRef(T* const State) throw() : m_State(State) {
    printf("(%p)AutoRef::AutoRef(%p)\n", (void*)this, (void*)State);
  }

  ~AutoRef() throw() {
    T::RefCount_XAdd(m_State, -1);
    printf("(%p)AutoRef::~AutoRef\n", (void*)this);
  }

public:
  AutoRef(AutoRef const&);
  AutoRef const& operator =(AutoRef const&);

public:
  void Cancel() const throw() {
    m_State = 0;
    printf("(%p)AutoRef::Cancel()\n", (void*)this);
  }

public:
  T* operator ->() const {
    if (! m_State) { throw std::exception(); }
    return m_State;
  }

  T& operator *() const {
    if (! m_State) { throw std::exception(); }
    return *m_State;
  }
};

class Foo {
  typedef AutoRef<Foo> AutoRef_t;

private:
  int m_RefCount;

public:
  typedef AutoRef_t const &Handle;

  static AutoRef_t Create() {
    Foo* const This = new Foo;
    printf("(%p)Foo::Create()\n", (void*)This);
    return AutoRef_t(This);
  }

private:
  static void Destroy(Foo* const This) {
    delete This;
    printf("(%p)Foo::Destroy()\n", (void*)This);
  }

public:
  Foo() : m_RefCount(1) {
    printf("(%p)Foo::Foo()\n", (void*)this);
  }

  ~Foo() throw() {
    printf("(%p)Foo::~Foo()\n", (void*)this);
  }

public:
  static void RefCount_XAdd(Foo* const This, int Count) {
    if (This) {
      --This->m_RefCount;
      printf("(%p)Foo::RefCount_XAdd(%d)\n", (void*)This, Count);
      if (This->m_RefCount < 1) {
        Destroy(This);
      }
    }
  }

public:
  void Test(int State) {
    printf("(%p)Foo::Test(%d)\n", (void*)this, State);
  }
};

int main() {
  {
    Foo::Handle Foo1 = Foo::Create();
    Foo1->Test(1);

    Foo::Handle Foo2 = Foo1;
    Foo2->Test(2);

    {
      Foo::Handle Foo3 = Foo1;
      Foo::Handle Foo4 = Foo2;
      Foo3->Test(3);
      Foo4->Test(4);
    }

    Foo1->Test(5);
    Foo2->Test(6);
  }

  printf("\n\n____________________\npress <ENTER> to exit...\n");
  getchar();
  return 0;
}

----------

Is this legitimate? Or, is the idea basically equal to a pile of pointless
crap!

Any thoughts?

:^)

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