ref.h

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        if (!managed()) return 1;
#       endif
        __REF_LOCK__(this);
#       if REF_CHECK_MIN_NREF
        if (_reference_count_ == 0) not_enough_refs();
#       endif
        _reference_count_--;
        refcount_t r = _reference_count_;
        __REF_UNLOCK__(this);
        return r;
      }

#if REF_MANAGE
    int managed() const {
        return _reference_count_ != REF_MANAGED_CODE;
      }
    /** Turn off the reference counting mechanism for this object.
        The value returned by nreference() will always be
        1 after this is called.  The ability to unmanage()
        objects must be turned on at compile time by defining
        REF_MANAGE.  There is a slight performance penalty. */
    void unmanage() {
        _reference_count_ = REF_MANAGED_CODE;
      }
#else // REF_MANAGE
    /// Return 1 if the object is managed.  Otherwise return 0.
    int managed() const { return 1; }
#endif // REF_MANAGE
};

/** Provides a few utility routines common to all
    Ref template instantiations.
*/
class RefBase {
  protected:
    /// Print a warning message.
    void warn ( const char * msg) const;
    /// Called when stack data is referenced.
    void warn_ref_to_stack() const;
    /// Called when the deletion of stack data is skipped.
    void warn_skip_stack_delete() const;
    /// Called when the reference count is corrupted.
    void warn_bad_ref_count() const;
    /// Print information about the reference.
    void ref_info(RefCount*p,std::ostream& os) const;
    void ref_info(std::ostream& os) const;
    void check_pointer() const;
    void reference(RefCount *);
    int dereference(RefCount *);
  public:
    virtual ~RefBase();
    /// Returns the DescribedClass pointer for the contained object.
    virtual RefCount* parentpointer() const = 0;
    /** Requires that a nonnull reference is held.  If not,
        the program will abort. */
    void require_nonnull() const;
};

/** A template class that maintains references counts.

    Several of these operations can cause a reference to an object to be
    replaced by a reference to a different object.  If a reference to a
    nonnull object is eliminated, the object's reference count is
    decremented and the object is deleted if the reference count becomes
    zero.

    There also may be a to convert to T*, where T is the type of the object
    which Ref references.  Some compilers have bugs that prevent the use of
    operator T*().  The pointer() member should be used instead.
 
*/
template <class T>
class  Ref  : public RefBase {
  private:
    T* p;
  public:
    /// Create a reference to a null object.
    Ref(): p(0) {}
    /// Create a reference to the object a.
    Ref(T*a) : p(0)
    {
      if (a) {
          p = a;
          reference(p);
        }
    }
    /// Create a reference to the object referred to by a.
    Ref(const Ref<T> &a) : p(0)
    {
      if (a.pointer()) {
          p = a.pointer();
          reference(p);
        }
    }
    /// Create a reference to the object referred to by a.
    template <class A> Ref(const Ref<A> &a): p(0)
    {
      if (a.pointer()) {
          p = a.pointer();
          reference(p);
        }
    }
//      /** Create a reference to the object a.  Do a
//          dynamic_cast to convert a to the appropiate type. */
//      Ref(const RefBase&a) {
//          p = dynamic_cast<T*>(a.parentpointer());
//          reference(p);
//        }
//      /** Create a reference to the object a.  Do a
//          dynamic_cast to convert a to the appropiate type. */
//      Ref(RefCount*a): p(0) {
//        operator<<(a);
//        }
    /** Delete this reference to the object.  Decrement the object's reference
        count and delete the object if the count is zero. */
    ~Ref()
    {
      clear();
    }
    /** Returns the reference counted object.  The behaviour is undefined if
        the object is null. */
    T* operator->() const { return p; }
    /// Returns a pointer the reference counted object.
    T* pointer() const { return p; }
    /// Implements the parentpointer pure virtual in the base class.
    RefCount *parentpointer() const { return p; }

    operator T*() const { return p; }
    /** Returns a C++ reference to the reference counted object.
        The behaviour is undefined if the object is null. */
    T& operator *() const { return *p; };
    /** Return 1 if this is a reference to a null object.  Otherwise
        return 0. */
    int null() const { return p == 0; }
    /// Return !null().
    int nonnull() const { return p != 0; }
    /** A variety of ordering and equivalence operators are provided using
        the Identity class. */
    template <class A> int operator==(const Ref<A>&a) const
        { return eq(p,a.pointer()); }
    template <class A> int operator>=(const Ref<A>&a) const
        { return ge(p,a.pointer()); }
    template <class A> int operator<=(const Ref<A>&a) const
        { return le(p,a.pointer()); }
    template <class A> int operator>(const Ref<A>&a) const
        { return gt(p,a.pointer()); }
    template <class A> int operator<(const Ref<A>&a) const
        { return lt(p,a.pointer()); }
    template <class A> int operator!=(const Ref<A>&a) const
        { return ne(p,a.pointer()); }
    /** Compare two objects returning -1, 0, or 1. Similar
        to the C library routine strcmp. */
    int compare(const Ref<T> &a) const {
      return eq(p,a.p)?0:((lt(p,a.p)?-1:1));
    }
    /// Refer to the null object.
    void clear()
    {
      if (p) {
          int ref = dereference(p);
          if (ref == 0)
              delete p;
          p = 0;
        }
    }
    /// Assignment to c.
    Ref<T>& operator=(const Ref<T> & c)
    {
      T *cp = c.pointer();
      if (cp) {
          cp->reference();
          clear();
          p=cp;
        }
      else {
          clear();
        }
      return *this;
    }
    /// Assignment to c.
    template <class A> Ref<T>& operator=(const Ref<A> & c)
    {
      A *cp = c.pointer();
      if (cp) {
          cp->reference();
          clear();
          p=cp;
        }
      else {
          clear();
        }
      return *this;
    }
    /// Assignment to the object that a references using dynamic_cast.
    Ref<T>& operator<<(const RefBase&a) {
        T* cr = dynamic_cast<T*>(a.parentpointer());
        if (cr) {
            reference(cr);
            clear();
          }
        p = cr;
        return *this;
      }
    /** Assigns to the given base class pointer using dynamic_cast.  If
        the dynamic_cast fails and the argument is nonnull and has a
        reference count of zero, then it is deleted. */
    Ref<T>& operator<<(RefCount *a) {
        T* cr = dynamic_cast<T*>(a);
        if (cr) assign_pointer(cr);
        else if (a && a->nreference() <= 0) delete a;
        return *this;
      }
    /// Assignment to cr.
    Ref<T>& operator=(T* cr)
    {
      assign_pointer(cr);
      return *this;
    }
    /// Assignment to cr.
    void assign_pointer(T* cr)
    {
      if (cr) {
          if (DO_REF_CHECK_STACK(cr)) {
              DO_REF_UNMANAGE(cr);
              warn_ref_to_stack();
            }
          cr->reference();
        }
      clear();
      p = cr;
    }
    /// Check the validity of the pointer.
    void check_pointer() const
    {
      if (p && p->nreference() <= 0) {
          warn_bad_ref_count();
        }
    }
    /// Print information about the reference to os.
    void ref_info(std::ostream& os) const
    {
      RefBase::ref_info(p,os);
    }
    /// Print a warning concerning the reference.
    void warn(const char*s) const { RefBase::warn(s); }
};

}

#endif

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