shared_ptr.hh

// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
// vi: set et ts=4 sw=2 sts=2:
// $Id: smartpointer.hh 5504 2009-04-08 13:35:31Z christi $

#ifndef DUNE_SHARED_PTR_HH
#define DUNE_SHARED_PTR_HH


#if defined HAVE_MEMORY
# include <memory>
#endif
#if defined HAVE_TR1_MEMORY
# include <tr1/memory>
#endif
#if defined HAVE_BOOST_SHARED_PTR_HPP
# include <boost/shared_ptr.hpp>
#endif

/**
 * @file
 * @brief This file implements the class shared_ptr (a reference counting
 * pointer), for those systems that don't have it in the standard library.
 * @author Markus Blatt
 */
namespace Dune
{
  // A shared_ptr implementation has been found if SHARED_PTR_NAMESPACE is set at all
#ifdef SHARED_PTR_NAMESPACE
  using SHARED_PTR_NAMESPACE :: shared_ptr;
#else

  /** @addtogroup Common
   *
   * @{
   */
  /**
   * @brief A reference counting smart pointer.
   *
   * It is designed such that it is usable within a std::vector.
   * The contained object is destroyed only if there are no more
   * references to it.
   */
  template<class T>
  class shared_ptr
  {
  public:
    /**
     * @brief The data type we are a pointer for.
     *
     * This has to have a parameterless constructor.
     */
    typedef T element_type;

    /**
     * @brief Constructs a new smart pointer and allocates the referenced Object.
     */
    inline shared_ptr();

    /**
     * @brief Constructs a new smart pointer from a preallocated Object.
     *
     * note: the object must be allocated on the heap and after handing the pointer to
     * shared_ptr the ownership of the pointer is also handed to the shared_ptr.
     */
    inline shared_ptr(T * pointer);

    /**
     * @brief Copy constructor.
     * @param pointer The object to copy.
     */
    inline shared_ptr(const shared_ptr<T>& pointer);

    /**
     * @brief Destructor.
     */
    inline ~shared_ptr();

    /** \brief Assignment operator */
    inline shared_ptr& operator=(const shared_ptr<T>& pointer);

    /** \brief Dereference as object */
    inline element_type& operator*();

    /** \brief Dereference as pointer */
    inline element_type* operator->();

    /** \brief Dereference as const object */
    inline const element_type& operator*() const;

    /** \brief Dereference as const pointer */
    inline const element_type* operator->() const;

    /** \brief Decrease the reference count by one and free the memory if the
        reference count has reached 0
     */
    inline void reset();

    /** \brief The number of shared_ptrs pointing to the object we point to */
    int use_count() const;

  private:
    /** @brief The object we reference. */
    class PointerRep
    {
      friend class shared_ptr<element_type>;
      /** @brief The number of references. */
      int count_;
      /** @brief The representative. */
      element_type * rep_;
      /** @brief Default Constructor. */
      PointerRep() : count_(1), rep_(new element_type) {}
      /** @brief Constructor from existing Pointer. */
      PointerRep(element_type * p) : count_(1), rep_(p) {}
      /** @brief Destructor, deletes element_type* rep_. */
      ~PointerRep() { delete rep_; }
    } *rep_;
  };

  template<class T>
  inline shared_ptr<T>::shared_ptr(T * p)
  {
    rep_ = new PointerRep(p);
  }

  template<class T>
  inline shared_ptr<T>::shared_ptr()
  {
    rep_ = NULL;
  }

  template<class T>
  inline shared_ptr<T>::shared_ptr(const shared_ptr<T>& other) : rep_(other.rep_)
  {
    ++(rep_->count_);
  }

  template<class T>
  inline shared_ptr<T>& shared_ptr<T>::operator=(const shared_ptr<T>& other)
  {
    (other.rep_->count_)++;
    if(rep_!=0 && --(rep_->count_)<=0) delete rep_;
    rep_ = other.rep_;
    return *this;
  }

  template<class T>
  inline shared_ptr<T>::~shared_ptr()
  {
    if(rep_!=0 && --(rep_->count_)==0) {
      delete rep_;
      rep_=0;
    }
  }

  template<class T>
  inline T& shared_ptr<T>::operator*()
  {
    return *(rep_->rep_);
  }

  template<class T>
  inline T *shared_ptr<T>::operator->()
  {
    return rep_->rep_;
  }

  template<class T>
  inline const T& shared_ptr<T>::operator*() const
  {
    return *(rep_->rep_);
  }

  template<class T>
  inline const T *shared_ptr<T>::operator->() const
  {
    return rep_->rep_;
  }

  template<class T>
  inline int shared_ptr<T>::use_count() const
  {
    return rep_->count_;
  }

  template<class T>
  inline void shared_ptr<T>::reset()
  {
    if(rep_!=0 && --(rep_->count_)==0) {
      delete rep_;
      rep_=0;
    }
  }

  /** @} */
#endif  // #ifdef SHARED_PTR_NAMESPACE

}
#endif