maybe.h

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// -*- mode: c++; tab-width: 4; indent-tabs-mode: t; eval: (progn (c-set-style "stroustrup") (c-set-offset 'innamespace 0)); -*-
// vi:set ts=4 sts=4 sw=4 noet :
//
// Copyright 2011, The TPIE development team
// 
// This file is part of TPIE.
// 
// TPIE is free software: you can redistribute it and/or modify it under
// the terms of the GNU Lesser General Public License as published by the
// Free Software Foundation, either version 3 of the License, or (at your
// option) any later version.
// 
// TPIE 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 Lesser General Public
// License for more details.
// 
// You should have received a copy of the GNU Lesser General Public License
// along with TPIE.  If not, see <http://www.gnu.org/licenses/>
 
 
#ifndef __TPIE_MAYBE_H__
#define __TPIE_MAYBE_H__
 
#include <tpie/exception.h>
#include <tpie/config.h>
 
namespace tpie {
 
template <typename T>
class maybe {
public:
    maybe() : m_constructed(false) {
    }
 
    maybe(const maybe<T> & o) : m_constructed(false) {
        o.assert_not_constructed();
    }
 
    maybe(maybe<T> && o) : m_constructed(false) {
        o.assert_not_constructed();
    }
 
private:
    void assert_not_constructed() const {
        if(m_constructed)
            throw maybe_exception("Maybe object already constructed");
    }
public:
 
    maybe & operator=(const maybe<T> &o) {
        o.assert_not_constructed();
        assert_not_constructed();
 
        return *this;
    }
 
    maybe & operator==(maybe<T> &o) {
        o.assert_not_constructed();
        assert_not_constructed();
 
        return *this;
    }
 
    bool is_constructed() const {
        return m_constructed;
    }
 
 
    template <typename ... T_ARGS>
    void construct(T_ARGS && ... args) {
        assert_not_constructed();
 
        new(&object) T(std::forward<T_ARGS>(args)...);
        m_constructed = true;
    }
 
    T & operator*() {
        return object;
    }
 
    const T & operator*() const {
        return object;
    }
 
    T * operator->() {
        return &object;
    }
 
    const T * operator->() const {
        return &object;
    }
 
    void destruct() {
        if(!m_constructed)
            return;
 
        object.~T();
        m_constructed = false;
    }
 
    ~maybe() {
        destruct();
    }
private:
    union { T object; };
    bool m_constructed;
};
} // namespace tpie
 
#endif