root/library/bdm/shared_ptr.h @ 477

/*!
  \file
  \brief BDM's own smart pointer.
  \author Vaclav Barta.

  -----------------------------------
  BDM++ - C++ library for Bayesian Decision Making under Uncertainty

  Using IT++ for numerical operations
  -----------------------------------
*/

#ifndef shared_ptr_h
#define shared_ptr_h

#include <limits.h>
#include <algorithm>
#include <stdexcept>
#include <string>
#include "itpp_ext.h"

namespace bdm {

//! A naive implementation of roughly a subset of the std::tr1:shared_ptr spec (really just roughly - it ignores memory exceptions, for example; also note I didn't read the spec).
// The standard template would naturally be preferable, _if_ it was
// included in the standard libraries of all supported compilers - but
// that's exactly what remains to be seen...
template <typename T>
class shared_ptr {
        template<class U> friend class shared_ptr;

private:
        T *payload;
        unsigned *refCnt;

public:
        //! Creates an empty shared_ptr - one that doesn't point anywhere.
        shared_ptr() :
                        payload ( 0 ),
                        refCnt ( 0 ) {
        }

        //! Constructs a shared_ptr that owns the pointer p (unless p is
        //! null, in which case this constructor creates an empty
        //! shared_ptr).
        shared_ptr ( T *p ) :
                        payload ( p ),
                        refCnt ( p ? new unsigned ( 1 ) : 0 ) {
        }

        //! If other is empty, constructs an empty shared_ptr; otherwise,
        //! constructs a shared_ptr that shares ownership with other.
        shared_ptr ( const shared_ptr<T> &other ) :
                        payload ( other.payload ),
                        refCnt ( other.refCnt ) {
                add_ref();
        }

        //! If other is empty, constructs an empty shared_ptr; otherwise,
        //! constructs a shared_ptr that shares ownership with other.
        template<typename U>
        shared_ptr ( const shared_ptr<U> &other ) :
                        payload ( other.payload ),
                        refCnt ( other.refCnt ) {
                add_ref();
        }

        ~shared_ptr() {
                del_ref();
        }

        shared_ptr &operator= ( const shared_ptr &other ) {
                other.add_ref();
                del_ref();

                payload = other.payload;
                refCnt = other.refCnt;

                return *this;
        }

        //! Returns the stored pointer (which remains owned by this
        //! instance).
        T *get() {
                return payload;
        }

        //! Returns the stored pointer (which remains owned by this
        //! instance). This method may only be called when the stored
        //! pointer isn't NULL.
        T *operator->() {
                it_assert_debug ( payload, "dereferencing NULL" );
                return payload;
        }

        //! Returns a reference to the object pointed to by the stored
        //! pointer. This method may only be called when the stored pointer
        //! isn't NULL.
        T &operator*() {
                it_assert_debug ( payload, "dereferencing NULL" );
                return *payload;
        }

        //! Returns the stored pointer (which remains owned by this
        //! instance).
        const T* get() const {
                return payload;
        }

        //! Returns the stored pointer (which remains owned by this
        //! instance). This method may only be called when the stored
        //! pointer isn't NULL.
        const T *operator->() const {
                it_assert_debug ( payload, "dereferencing NULL" );
                return payload;
        }

        //! Returns a reference to the object pointed to by the stored
        //! pointer. This method may only be called when the stored pointer
        //! isn't NULL.
        const T &operator*() const {
                it_assert_debug ( payload, "dereferencing NULL" );
                return *payload;
        }

        bool unique() const {
                return refCnt && ( *refCnt == 1 );
        }

        long use_count() const {
                return refCnt ? *refCnt : 0;
        }

        operator bool() const {
                return payload;
        }

        void swap ( shared_ptr &other ) {
                std::swap ( payload, other.payload );
                std::swap ( refCnt, other.refCnt );
        }

private:
        void add_ref() const {
                if ( refCnt ) {
                        if ( *refCnt == UINT_MAX ) {
                                throw std::overflow_error (
                                    std::string ( "Shared pointer has too many references." ) );
                        }

                        ++*refCnt;
                }
        }

        void del_ref() {
                if ( refCnt ) {
                        if ( ! ( --*refCnt ) ) {
                                delete payload;
                                delete refCnt;
                        }
                }
        }
};

template<typename T, typename U>
bool operator== ( shared_ptr<T> const &a, shared_ptr<U> const &b ) {
        return a.get() == b.get();
}

template<typename T, typename U>
bool operator!= ( shared_ptr<T> const &a, shared_ptr<U> const &b ) {
        return a.get() != b.get();
}

template<typename T, typename U>
bool operator< ( shared_ptr<T> const &a, shared_ptr<U> const &b ) {
        return a.get() < b.get();
}

}

#endif