ptr.h

Go to the documentation of this file.

/*
 *  GiNaC Copyright (C) 1999-2011 Johannes Gutenberg University Mainz, Germany
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 */

#ifndef GINAC_PTR_H
#define GINAC_PTR_H

#include "assertion.h"

#include <cstddef> // for size_t
#include <functional>
#include <iosfwd>

namespace GiNaC {

class refcounted {
public:
    refcounted() throw() : refcount(0) {}

    unsigned int add_reference() throw() { return ++refcount; }
    unsigned int remove_reference() throw() { return --refcount; }
    unsigned int get_refcount() const throw() { return refcount; }
    void set_refcount(unsigned int r) throw() { refcount = r; }

private:
    unsigned int refcount; 
};


template <class T> class ptr {
    friend class std::less< ptr<T> >;

    // NB: This implementation of reference counting is not thread-safe.
    // The reference counter needs to be incremented/decremented atomically,
    // and makewritable() requires locking.

public:
    // no default ctor: a ptr is never unbound

    ptr(T *t) throw() : p(t) { GINAC_ASSERT(p); p->set_refcount(1); }

    explicit ptr(T &t) throw() : p(&t) { p->add_reference(); }

    ptr(const ptr & other) throw() : p(other.p) { p->add_reference(); }

    ~ptr()
    {
        if (p->remove_reference() == 0)
            delete p;
    }

    ptr &operator=(const ptr & other)
    {
        // NB1: Must first add reference to "other", since other might be *this.
        // NB2: Cache other.p, because if "other" is a subexpression of p,
        //      deleting p will also invalidate "other".
        T *otherp = other.p;
        otherp->add_reference();
        if (p->remove_reference() == 0)
            delete p;
        p = otherp;
        return *this;
    }

    T &operator*() const throw() { return *p; }
    T *operator->() const throw() { return p; }

    friend inline T *get_pointer(const ptr & x) throw() { return x.p; }

    void makewritable()
    {
        if (p->get_refcount() > 1) {
            T *p2 = p->duplicate();
            p2->set_refcount(1);
            p->remove_reference();
            p = p2;
        }
    }

    void swap(ptr & other) throw()
    {
        T *t = p;
        p = other.p;
        other.p = t;
    }

    // ptr<>s are always supposed to be bound to a valid object, so we don't
    // provide support for "if (p)", "if (!p)", "if (p==0)" and "if (p!=0)".
    // We do, however, provide support for comparing ptr<>s with other ptr<>s
    // to different (probably derived) types and raw pointers.

    template <class U>
    bool operator==(const ptr<U> & rhs) const throw() { return p == get_pointer(rhs); }

    template <class U>
    bool operator!=(const ptr<U> & rhs) const throw() { return p != get_pointer(rhs); }

    template <class U>
    inline friend bool operator==(const ptr & lhs, const U * rhs) throw() { return lhs.p == rhs; }

    template <class U>
    inline friend bool operator!=(const ptr & lhs, const U * rhs) throw() { return lhs.p != rhs; }

    template <class U>
    inline friend bool operator==(const U * lhs, const ptr & rhs) throw() { return lhs == rhs.p; }

    template <class U>
    inline friend bool operator!=(const U * lhs, const ptr & rhs) throw() { return lhs != rhs.p; }

    inline friend std::ostream & operator<<(std::ostream & os, const ptr<T> & rhs)
    {
        os << rhs.p;
        return os;
    }

private:
    T *p;
};

} // namespace GiNaC


namespace std {

template <class T> struct less< GiNaC::ptr<T> >
 : public binary_function<GiNaC::ptr<T>, GiNaC::ptr<T>, bool> {
    bool operator()(const GiNaC::ptr<T> &lhs, const GiNaC::ptr<T> &rhs) const
    {
        return less<T*>()(lhs.p, rhs.p);
    }
};

} // namespace std

#endif // ndef GINAC_PTR_H