ptr.h

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/*
 *  GiNaC Copyright (C) 1999-2023 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() noexcept : refcount(0) {}
 
    unsigned int add_reference() noexcept { return ++refcount; }
    unsigned int remove_reference() noexcept { return --refcount; }
    unsigned int get_refcount() const noexcept { return refcount; }
    void set_refcount(unsigned int r) noexcept { refcount = r; }
 
private:
    unsigned int refcount; 
};
 
 
template <class T> class ptr {
    friend struct 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) noexcept : p(t) { GINAC_ASSERT(p); p->set_refcount(1); }
 
    explicit ptr(T &t) noexcept : p(&t) { p->add_reference(); }
 
    ptr(const ptr & other) noexcept : 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 noexcept { return *p; }
    T *operator->() const noexcept { return p; }
 
    friend inline T *get_pointer(const ptr & x) noexcept { 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) noexcept
    {
        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 noexcept { return p == get_pointer(rhs); }
 
    template <class U>
    bool operator!=(const ptr<U> & rhs) const noexcept { return p != get_pointer(rhs); }
 
    template <class U>
    inline friend bool operator==(const ptr & lhs, const U * rhs) noexcept { return lhs.p == rhs; }
 
    template <class U>
    inline friend bool operator!=(const ptr & lhs, const U * rhs) noexcept { return lhs.p != rhs; }
 
    template <class U>
    inline friend bool operator==(const U * lhs, const ptr & rhs) noexcept { return lhs == rhs.p; }
 
    template <class U>
    inline friend bool operator!=(const U * lhs, const ptr & rhs) noexcept { 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>> {
    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