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more/gen/null_container.h

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//  Copyright (C) 2001  Petter Urkedal (petter.urkedal@matfys.lth.se)
//
//  This file 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 file 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., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//
//  As a special exception, you may use this file as part of a free
//  software library without restriction.  Specifically, if other files
//  instantiate templates or use macros or inline functions from this
//  file, or you compile this file and link it with other files to
//  produce an executable, this file does not by itself cause the
//  resulting executable to be covered by the GNU General Public
//  License.  This exception does not however invalidate any other
//  reasons why the executable file might be covered by the GNU General
//  Public License.
//
//  $Id: null_container.h,v 1.1 2002/05/30 18:01:37 petter_urkedal Exp $


#ifndef MORE_GEN_NULL_CONTAINER_H
#define MORE_GEN_NULL_CONTAINER_H


#include <iterator>
#include <stdexcept>


namespace more {
namespace gen {

  /** \class null_iterator null_container.h more/gen/null_container.h
   *  A random access iterator with only one value, a past-the-end
   *  iterator. */
  template<typename Value>
    struct null_iterator {
        typedef std::random_access_iterator_tag iterator_category;
        typedef std::ptrdiff_t difference_type;
        typedef Value value_type;
        typedef value_type& reference;
        typedef value_type* pointer;

        null_iterator() {}
        // Provide conversion from the const valued iterator, or if
        // value is const, this just redundantly define the copy ctor
        // and assignment.
        null_iterator(null_iterator<Value const> const&) {}
        null_iterator& operator=(null_iterator<Value const> const&) {
            return *this;
        }

        null_iterator& operator++() { return *this; }
        null_iterator& operator++(int) { return *this; }
        null_iterator& operator--() { return *this; }
        null_iterator& operator--(int) { return *this; }
        null_iterator& operator+=(difference_type) { return *this; }
        null_iterator& operator-=(difference_type) { return *this; }
        null_iterator operator+(difference_type) { return *this; }
        null_iterator operator-(difference_type) { return *this; }
        friend null_iterator
          operator+(difference_type, null_iterator x) { return x; }
        difference_type operator-(null_iterator) { return 0; }

        bool operator==(null_iterator const&) const { return true; }
        bool operator!=(null_iterator const&) const { return false; }
        bool operator<(null_iterator const&) const { return false; }
        bool operator>(null_iterator const&) const { return false; }
        bool operator<=(null_iterator const&) const { return true; }
        bool operator>=(null_iterator const&) const { return true; }

        reference operator*() {
            throw std::logic_error("Dereference of past-the-end iterator.");
        }
        pointer operator->() { return &**this; }
        reference operator[](difference_type) { return **this; }
    };

  /** \class null_container null_container.h more/gen/null_container.h
   *  A container which is always empty. */
  template<typename Value>
    struct null_container {
        typedef Value value_type;
        typedef value_type& reference;
        typedef value_type const& const_reference;
        typedef null_iterator<value_type> iterator;
        typedef null_iterator<value_type const> const_iterator;
        typedef std::ptrdiff_t difference_type;
        typedef std::size_t size_type;

        null_container() {}
        // null_container(null_container const&); implied
        // null_container& operator=(null_container const&); implied
        const_iterator begin() const { return const_iterator(); }
        const_iterator end() const { return const_iterator(); }
        iterator begin() { return iterator(); }
        iterator end() { return iterator(); }

        bool operator==(null_container const&) const { return true; }
        bool operator!=(null_container const&) const { return false; }
        void swap(null_container&) {}
    };
}} // more::gen

#endif

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