[857] | 1 | // Copyright Vladimir Prus 2004.
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| 2 | // Distributed under the Boost Software License, Version 1.0.
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| 3 | // (See accompanying file LICENSE_1_0.txt
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| 4 | // or copy at http://www.boost.org/LICENSE_1_0.txt)
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| 5 |
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| 6 | #ifndef BOOST_EOF_ITERATOR_VP_2004_03_12
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| 7 | #define BOOST_EOF_ITERATOR_VP_2004_03_12
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| 8 |
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| 9 | #include <boost/iterator/iterator_facade.hpp>
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| 10 |
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| 11 | namespace boost {
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| 12 |
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| 13 | /** The 'eof_iterator' class is useful for constructing forward iterators
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| 14 | in cases where iterator extract data from some source and it's easy
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| 15 | to detect 'eof' -- i.e. the situation where there's no data. One
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| 16 | apparent example is reading lines from a file.
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| 17 |
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| 18 | Implementing such iterators using 'iterator_facade' directly would
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| 19 | require to create class with three core operation, a couple of
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| 20 | constructors. When using 'eof_iterator', the derived class should define
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| 21 | only one method to get new value, plus a couple of constructors.
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| 22 |
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| 23 | The basic idea is that iterator has 'eof' bit. Two iterators are equal
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| 24 | only if both have their 'eof' bits set. The 'get' method either obtains
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| 25 | the new value or sets the 'eof' bit.
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| 26 |
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| 27 | Specifically, derived class should define:
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| 28 |
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| 29 | 1. A default constructor, which creates iterator with 'eof' bit set. The
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| 30 | constructor body should call 'found_eof' method defined here.
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| 31 | 2. Some other constructor. It should initialize some 'data pointer' used
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| 32 | in iterator operation and then call 'get'.
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| 33 | 3. The 'get' method. It should operate this way:
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| 34 | - look at some 'data pointer' to see if new element is available;
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| 35 | if not, it should call 'found_eof'.
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| 36 | - extract new element and store it at location returned by the 'value'
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| 37 | method.
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| 38 | - advance the data pointer.
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| 39 |
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| 40 | Essentially, the 'get' method has the functionality of both 'increment'
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| 41 | and 'dereference'. It's very good for the cases where data extraction
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| 42 | implicitly moves data pointer, like for stream operation.
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| 43 | */
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| 44 | template<class Derived, class ValueType>
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| 45 | class eof_iterator : public iterator_facade<Derived, const ValueType,
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| 46 | forward_traversal_tag>
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| 47 | {
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| 48 | public:
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| 49 | eof_iterator()
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| 50 | : m_at_eof(false)
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| 51 | {}
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| 52 |
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| 53 | protected: // interface for derived
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| 54 |
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| 55 | /** Returns the reference which should be used by derived
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| 56 | class to store the next value. */
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| 57 | ValueType& value()
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| 58 | {
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| 59 | return m_value;
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| 60 | }
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| 61 |
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| 62 | /** Should be called by derived class to indicate that it can't
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| 63 | produce next element. */
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| 64 | void found_eof()
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| 65 | {
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| 66 | m_at_eof = true;
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| 67 | }
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| 68 |
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| 69 |
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| 70 | private: // iterator core operations
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| 71 | friend class iterator_core_access;
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| 72 |
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| 73 | void increment()
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| 74 | {
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| 75 | static_cast<Derived&>(*this).get();
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| 76 | }
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| 77 |
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| 78 | bool equal(const eof_iterator& other) const
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| 79 | {
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| 80 | if (m_at_eof && other.m_at_eof)
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| 81 | return true;
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| 82 | else
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| 83 | return false;
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| 84 | }
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| 85 |
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| 86 | const ValueType& dereference() const
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| 87 | {
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| 88 | return m_value;
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| 89 | }
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| 90 |
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| 91 | bool m_at_eof;
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| 92 | ValueType m_value;
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| 93 | };
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| 94 | }
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| 95 |
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| 96 | #endif
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| 97 |
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