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singleton.h

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00001 // -*- C++ -*-
00002 #ifndef WIBBLE_SINGLETON_H
00003 #define WIBBLE_SINGLETON_H
00004 
00005 /*
00006  * Degenerated container to hold a single value
00007  *
00008  * Copyright (C) 2006  Enrico Zini <enrico@debian.org>
00009  *
00010  * This library is free software; you can redistribute it and/or
00011  * modify it under the terms of the GNU Lesser General Public
00012  * License as published by the Free Software Foundation; either
00013  * version 2.1 of the License, or (at your option) any later version.
00014  *
00015  * This library is distributed in the hope that it will be useful,
00016  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00017  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00018  * Lesser General Public License for more details.
00019  *
00020  * You should have received a copy of the GNU Lesser General Public
00021  * License along with this library; if not, write to the Free Software
00022  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
00023  */
00024 
00025 #include <cstddef>
00026 #include <bits/stl_iterator_base_types.h>
00027 
00028 #include <cstddef>
00029 #include <bits/stl_iterator_base_types.h>
00030 
00031 namespace wibble {
00032 
00033 template<typename T>
00034 class Singleton
00035 {
00036 protected:
00037     T value;
00038 
00039 public:
00040     typedef T value_type;
00041 
00042     class const_iterator : public std::iterator<std::forward_iterator_tag, const T, void, const T*, const T&>
00043     {
00044         const T* value;
00045 
00046     protected:
00047         const_iterator(const T* value) : value(value) {}
00048 
00049     public:
00050         const_iterator() : value(0) {}
00051 
00052         const T& operator*() const { return *value; }
00053         const T* operator->() const { return value; }
00054         const_iterator& operator++() { value = 0; return *this; }
00055         bool operator==(const const_iterator& iter) const { return value == iter.value; }
00056         bool operator!=(const const_iterator& iter) const { return value != iter.value; }
00057 
00058         friend class Singleton<T>;
00059     };
00060 
00061     class iterator : public std::iterator<std::forward_iterator_tag, T, void, T*, T&>
00062     {
00063         T* value;
00064 
00065     protected:
00066         iterator(T* value) : value(value) {}
00067 
00068     public:
00069         iterator() : value(0) {}
00070 
00071         T& operator*() { return *value; }
00072         T* operator->() { return value; }
00073         iterator& operator++() { value = 0; return *this; }
00074         bool operator==(const iterator& iter) const { return value == iter.value; }
00075         bool operator!=(const iterator& iter) const { return value != iter.value; }
00076 
00077         friend class Singleton<T>;
00078     };
00079 
00080     explicit Singleton(const T& value) : value(value) {}
00081 
00082     bool empty() const { return false; }
00083     size_t size() const { return 1; }
00084 
00085     iterator begin() { return iterator(&value); }
00086     iterator end() { return iterator(); }
00087     const_iterator begin() const { return const_iterator(&value); }
00088     const_iterator end() const { return const_iterator(); }
00089 };
00090 
00091 template<typename T>
00092 Singleton<T> singleton(const T& value)
00093 {
00094     return Singleton<T>(value);
00095 }
00096 
00097 }
00098 
00099 // vim:set ts=4 sw=4:
00100 #endif

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