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