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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 | friend class iterator_core_access; | |
72 | ||
73 | void increment() | |
74 | { | |
75 | static_cast<Derived&>(*this).get(); | |
76 | } | |
77 | ||
78 | bool equal(const eof_iterator& other) const | |
79 | { | |
80 | if (m_at_eof && other.m_at_eof) | |
81 | return true; | |
82 | else | |
83 | return false; | |
84 | } | |
85 | ||
86 | const ValueType& dereference() const | |
87 | { | |
88 | return m_value; | |
89 | } | |
90 | ||
91 | bool m_at_eof; | |
92 | ValueType m_value; | |
93 | }; | |
94 | } | |
95 | ||
96 | #endif | |
97 |