1 | // Copyright Vladimir Prus 2004. |
2 | // Distributed under the Boost Software License, Version 1.0. |
3 | // (See accompanying file LICENSE_1_0.txt |
4 | // or copy at http://www.boost.org/LICENSE_1_0.txt) |
5 | |
6 | #ifndef BOOST_EOF_ITERATOR_VP_2004_03_12 |
7 | #define BOOST_EOF_ITERATOR_VP_2004_03_12 |
8 | |
9 | #include <boost/iterator/iterator_facade.hpp> |
10 | |
11 | namespace boost { |
12 | |
13 | /** The 'eof_iterator' class is useful for constructing forward iterators |
14 | in cases where iterator extract data from some source and it's easy |
15 | to detect 'eof' \-- i.e. the situation where there's no data. One |
16 | apparent example is reading lines from a file. |
17 | |
18 | Implementing such iterators using 'iterator_facade' directly would |
19 | require to create class with three core operation, a couple of |
20 | constructors. When using 'eof_iterator', the derived class should define |
21 | only one method to get new value, plus a couple of constructors. |
22 | |
23 | The basic idea is that iterator has 'eof' bit. Two iterators are equal |
24 | only if both have their 'eof' bits set. The 'get' method either obtains |
25 | the new value or sets the 'eof' bit. |
26 | |
27 | Specifically, derived class should define: |
28 | |
29 | 1. A default constructor, which creates iterator with 'eof' bit set. The |
30 | constructor body should call 'found_eof' method defined here. |
31 | 2. Some other constructor. It should initialize some 'data pointer' used |
32 | in iterator operation and then call 'get'. |
33 | 3. The 'get' method. It should operate this way: |
34 | - look at some 'data pointer' to see if new element is available; |
35 | if not, it should call 'found_eof'. |
36 | - extract new element and store it at location returned by the 'value' |
37 | method. |
38 | - advance the data pointer. |
39 | |
40 | Essentially, the 'get' method has the functionality of both 'increment' |
41 | and 'dereference'. It's very good for the cases where data extraction |
42 | implicitly moves data pointer, like for stream operation. |
43 | */ |
44 | template<class Derived, class ValueType> |
45 | class eof_iterator : public iterator_facade<Derived, const ValueType, |
46 | forward_traversal_tag> |
47 | { |
48 | public: |
49 | eof_iterator() |
50 | : m_at_eof(false) |
51 | {} |
52 | |
53 | protected: // interface for derived |
54 | |
55 | /** Returns the reference which should be used by derived |
56 | class to store the next value. */ |
57 | ValueType& value() |
58 | { |
59 | return m_value; |
60 | } |
61 | |
62 | /** Should be called by derived class to indicate that it can't |
63 | produce next element. */ |
64 | void found_eof() |
65 | { |
66 | m_at_eof = true; |
67 | } |
68 | |
69 | |
70 | private: // iterator core operations |
71 | #ifdef __DCC__ |
72 | friend class boost::iterator_core_access; |
73 | #else |
74 | friend class iterator_core_access; |
75 | #endif |
76 | |
77 | void increment() |
78 | { |
79 | static_cast<Derived&>(*this).get(); |
80 | } |
81 | |
82 | bool equal(const eof_iterator& other) const |
83 | { |
84 | if (m_at_eof && other.m_at_eof) |
85 | return true; |
86 | else |
87 | return false; |
88 | } |
89 | |
90 | const ValueType& dereference() const |
91 | { |
92 | return m_value; |
93 | } |
94 | |
95 | bool m_at_eof; |
96 | ValueType m_value; |
97 | }; |
98 | } |
99 | |
100 | #endif |
101 | |
102 | |