wibble  0.1.28
singleton.h
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1 // -*- C++ -*-
2 #ifndef WIBBLE_SINGLETON_H
3 #define WIBBLE_SINGLETON_H
4 
5 /*
6  * Degenerated container to hold a single value
7  *
8  * Copyright (C) 2006 Enrico Zini <enrico@debian.org>
9  *
10  * This library is free software; you can redistribute it and/or
11  * modify it under the terms of the GNU Lesser General Public
12  * License as published by the Free Software Foundation; either
13  * version 2.1 of the License, or (at your option) any later version.
14  *
15  * This library is distributed in the hope that it will be useful,
16  * but WITHOUT ANY WARRANTY; without even the implied warranty of
17  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18  * Lesser General Public License for more details.
19  *
20  * You should have received a copy of the GNU Lesser General Public
21  * License along with this library; if not, write to the Free Software
22  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
23  */
24 
25 #include <cstddef>
26 #include <iterator>
27 
28 namespace wibble {
29 
30 template<typename T>
31 class Singleton
32 {
33 protected:
34  T value;
35 
36 public:
37  typedef T value_type;
38 
39  class const_iterator : public std::iterator<std::forward_iterator_tag, const T, void, const T*, const T&>
40  {
41  const T* value;
42 
43  protected:
44  const_iterator(const T* value) : value(value) {}
45 
46  public:
47  const_iterator() : value(0) {}
48 
49  const T& operator*() const { return *value; }
50  const T* operator->() const { return value; }
51  const_iterator& operator++() { value = 0; return *this; }
52  bool operator==(const const_iterator& iter) const { return value == iter.value; }
53  bool operator!=(const const_iterator& iter) const { return value != iter.value; }
54 
55  friend class Singleton<T>;
56  };
57 
58  class iterator : public std::iterator<std::forward_iterator_tag, T, void, T*, T&>
59  {
60  T* value;
61 
62  protected:
63  iterator(T* value) : value(value) {}
64 
65  public:
66  iterator() : value(0) {}
67 
68  T& operator*() { return *value; }
69  T* operator->() { return value; }
70  iterator& operator++() { value = 0; return *this; }
71  bool operator==(const iterator& iter) const { return value == iter.value; }
72  bool operator!=(const iterator& iter) const { return value != iter.value; }
73 
74  friend class Singleton<T>;
75  };
76 
77  explicit Singleton(const T& value) : value(value) {}
78 
79  bool empty() const { return false; }
80  size_t size() const { return 1; }
81 
82  iterator begin() { return iterator(&value); }
83  iterator end() { return iterator(); }
84  const_iterator begin() const { return const_iterator(&value); }
85  const_iterator end() const { return const_iterator(); }
86 };
87 
88 template<typename T>
89 Singleton<T> singleton(const T& value)
90 {
91  return Singleton<T>(value);
92 }
93 
94 }
95 
96 // vim:set ts=4 sw=4:
97 #endif