98 lines
3.3 KiB
Plaintext
98 lines
3.3 KiB
Plaintext
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// Copyright Vladimir Prus 2004.
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// Distributed under the Boost Software License, Version 1.0.
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// (See accompanying file LICENSE_1_0.txt
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// or copy at http://www.boost.org/LICENSE_1_0.txt)
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#ifndef BOOST_EOF_ITERATOR_VP_2004_03_12
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#define BOOST_EOF_ITERATOR_VP_2004_03_12
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#include <boost/iterator/iterator_facade.hpp>
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namespace boost {
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/** The 'eof_iterator' class is useful for constructing forward iterators
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in cases where iterator extract data from some source and it's easy
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to detect 'eof' \-- i.e. the situation where there's no data. One
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apparent example is reading lines from a file.
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Implementing such iterators using 'iterator_facade' directly would
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require to create class with three core operation, a couple of
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constructors. When using 'eof_iterator', the derived class should define
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only one method to get new value, plus a couple of constructors.
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The basic idea is that iterator has 'eof' bit. Two iterators are equal
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only if both have their 'eof' bits set. The 'get' method either obtains
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the new value or sets the 'eof' bit.
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Specifically, derived class should define:
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1. A default constructor, which creates iterator with 'eof' bit set. The
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constructor body should call 'found_eof' method defined here.
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2. Some other constructor. It should initialize some 'data pointer' used
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in iterator operation and then call 'get'.
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3. The 'get' method. It should operate this way:
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- look at some 'data pointer' to see if new element is available;
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if not, it should call 'found_eof'.
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- extract new element and store it at location returned by the 'value'
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method.
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- advance the data pointer.
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Essentially, the 'get' method has the functionality of both 'increment'
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and 'dereference'. It's very good for the cases where data extraction
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implicitly moves data pointer, like for stream operation.
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*/
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template<class Derived, class ValueType>
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class eof_iterator : public iterator_facade<Derived, const ValueType,
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forward_traversal_tag>
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{
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public:
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eof_iterator()
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: m_at_eof(false)
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{}
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protected: // interface for derived
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/** Returns the reference which should be used by derived
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class to store the next value. */
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ValueType& value()
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{
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return m_value;
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}
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/** Should be called by derived class to indicate that it can't
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produce next element. */
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void found_eof()
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{
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m_at_eof = true;
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}
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private: // iterator core operations
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friend class iterator_core_access;
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void increment()
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{
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static_cast<Derived&>(*this).get();
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}
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bool equal(const eof_iterator& other) const
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{
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if (m_at_eof && other.m_at_eof)
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return true;
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else
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return false;
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}
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const ValueType& dereference() const
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{
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return m_value;
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}
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bool m_at_eof;
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ValueType m_value;
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};
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}
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#endif
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