// 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 | |