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329 lines
9.6 KiB
Plaintext
329 lines
9.6 KiB
Plaintext
[/
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Copyright 2010 Neil Groves
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Distributed under the Boost Software License, Version 1.0.
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(See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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/]
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[section:extending Extending the library]
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[section:method_1 Method 1: provide member functions and nested types]
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This procedure assumes that you have control over the types that should be made conformant to a Range concept. If not, see [link range.reference.extending.method_2 method 2].
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The primary templates in this library are implemented such that standard containers will work automatically and so will __boost_array__. Below is given an overview of which member functions and member types a class must specify to be useable as a certain Range concept.
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[table
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[[Member function] [Related concept ]]
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[[`begin()` ] [__single_pass_range__]]
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[[`end()` ] [__single_pass_range__]]
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]
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Notice that `rbegin()` and `rend()` member functions are not needed even though the container can support bidirectional iteration.
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The required member types are:
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[table
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[[Member type ] [Related concept ]]
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[[`iterator` ] [__single_pass_range__]]
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[[`const_iterator`] [__single_pass_range__]]
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]
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Again one should notice that member types `reverse_iterator` and `const_reverse_iterator` are not needed.
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[endsect]
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[section:method_2 Method 2: provide free-standing functions and specialize metafunctions]
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This procedure assumes that you cannot (or do not wish to) change the types that should be made conformant to a Range concept. If this is not true, see [link range.reference.extending.method_1 method 1].
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The primary templates in this library are implemented such that certain functions are found via argument-dependent-lookup (ADL). Below is given an overview of which free-standing functions a class must specify to be useable as a certain Range concept. Let `x` be a variable (`const` or `mutable`) of the class in question.
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[table
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[[Function ] [Related concept ]]
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[[`range_begin(x)`] [__single_pass_range__]]
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[[`range_end(x)` ] [__single_pass_range__]]
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[[`range_calculate_size(x)`] [ Optional. This can be used to specify a mechanism for constant-time computation of the size of a range. The default behaviour is to return `boost::end(x) - boost::begin(x)` for random access ranges, and to return `x.size()` for ranges with lesser traversal capability. This behaviour can be changed by implementing `range_calculate_size` in a manner that will be found via ADL. The ability to calculate size in O(1) is often possible even with ranges with traversal categories less than random access.]]
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]
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`range_begin()` and `range_end()` must be overloaded for both `const` and `mutable` reference arguments.
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You must also specialize two metafunctions for your type `X`:
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[table
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[[Metafunction ] [Related concept ]]
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[[`boost::range_mutable_iterator`] [__single_pass_range__]]
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[[`boost::range_const_iterator`] [__single_pass_range__]]
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]
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A complete example is given here:
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``
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#include <boost/range.hpp>
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#include <iterator> // for std::iterator_traits, std::distance()
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namespace Foo
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{
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//
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// Our sample UDT. A 'Pair'
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// will work as a range when the stored
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// elements are iterators.
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//
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template< class T >
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struct Pair
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{
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T first, last;
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};
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} // namespace 'Foo'
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namespace boost
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{
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//
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// Specialize metafunctions. We must include the range.hpp header.
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// We must open the 'boost' namespace.
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//
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template< class T >
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struct range_mutable_iterator< Foo::Pair<T> >
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{
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typedef T type;
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};
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template< class T >
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struct range_const_iterator< Foo::Pair<T> >
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{
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//
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// Remark: this is defined similar to 'range_iterator'
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// because the 'Pair' type does not distinguish
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// between an iterator and a const_iterator.
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//
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typedef T type;
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};
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} // namespace 'boost'
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namespace Foo
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{
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//
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// The required functions. These should be defined in
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// the same namespace as 'Pair', in this case
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// in namespace 'Foo'.
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//
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template< class T >
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inline T range_begin( Pair<T>& x )
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{
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return x.first;
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}
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template< class T >
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inline T range_begin( const Pair<T>& x )
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{
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return x.first;
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}
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template< class T >
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inline T range_end( Pair<T>& x )
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{
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return x.last;
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}
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template< class T >
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inline T range_end( const Pair<T>& x )
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{
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return x.last;
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}
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} // namespace 'Foo'
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#include <vector>
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int main(int argc, const char* argv[])
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{
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typedef std::vector<int>::iterator iter;
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std::vector<int> vec;
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Foo::Pair<iter> pair = { vec.begin(), vec.end() };
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const Foo::Pair<iter>& cpair = pair;
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//
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// Notice that we call 'begin' etc with qualification.
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//
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iter i = boost::begin( pair );
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iter e = boost::end( pair );
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i = boost::begin( cpair );
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e = boost::end( cpair );
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boost::range_difference< Foo::Pair<iter> >::type s = boost::size( pair );
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s = boost::size( cpair );
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boost::range_reverse_iterator< const Foo::Pair<iter> >::type
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ri = boost::rbegin( cpair ),
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re = boost::rend( cpair );
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return 0;
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}
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``
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[endsect]
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[section:method_3 Method 3: provide range adaptor implementations]
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[section:method_3_1 Method 3.1: Implement a Range Adaptor without arguments]
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To implement a Range Adaptor without arguments (e.g. reversed) you need to:
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# Provide a range for your return type, for example:
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``
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#include <boost/range/iterator_range.hpp>
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#include <boost/iterator/reverse_iterator.hpp>
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template< typename R >
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struct reverse_range :
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boost::iterator_range<
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boost::reverse_iterator<
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typename boost::range_iterator<R>::type> >
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{
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private:
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typedef boost::iterator_range<
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boost::reverse_iterator<
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typename boost::range_iterator<R>::type> > base;
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public:
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typedef boost::reverse_iterator<
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typename boost::range_iterator<R>::type > iterator;
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reverse_range(R& r)
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: base(iterator(boost::end(r)), iterator(boost::begin(r)))
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{ }
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};
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``
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# Provide a tag to uniquely identify your adaptor in the `operator|` function overload set
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``
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namespace detail {
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struct reverse_forwarder {};
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}
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``
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# Implement `operator|`
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``
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template< class BidirectionalRng >
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inline reverse_range<BidirectionalRng>
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operator|( BidirectionalRng& r, detail::reverse_forwarder )
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{
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return reverse_range<BidirectionalRng>( r );
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}
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template< class BidirectionalRng >
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inline reverse_range<const BidirectionalRng>
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operator|( const BidirectionalRng& r, detail::reverse_forwarder )
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{
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return reverse_range<const BidirectionalRng>( r );
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}
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``
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# Declare the adaptor itself (it is a variable of the tag type).
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``
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namespace
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{
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const detail::reverse_forwarder reversed = detail::reverse_forwarder();
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}
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``
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[endsect]
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[section:method_3_2 Method 3.2: Implement a Range Adaptor with arguments]
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# Provide a range for your return type, for example:
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``
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#include <boost/range/adaptor/argument_fwd.hpp>
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#include <boost/range/iterator_range.hpp>
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#include <boost/iterator/transform_iterator.hpp>
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template<typename Value>
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class replace_value
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{
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public:
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typedef const Value& result_type;
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typedef const Value& argument_type;
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replace_value(const Value& from, const Value& to)
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: m_from(from), m_to(to)
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{
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}
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const Value& operator()(const Value& x) const
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{
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return (x == m_from) ? m_to : x;
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}
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private:
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Value m_from;
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Value m_to;
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};
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template<typename Range>
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class replace_range
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: public boost::iterator_range<
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boost::transform_iterator<
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replace_value<typename boost::range_value<Range>::type>,
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typename boost::range_iterator<Range>::type> >
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{
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private:
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typedef typename boost::range_value<Range>::type value_type;
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typedef typename boost::range_iterator<Range>::type iterator_base;
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typedef replace_value<value_type> Fn;
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typedef boost::transform_iterator<Fn, iterator_base> replaced_iterator;
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typedef boost::iterator_range<replaced_iterator> base_t;
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public:
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replace_range(Range& rng, value_type from, value_type to)
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: base_t(replaced_iterator(boost::begin(rng), Fn(from,to)),
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replaced_iterator(boost::end(rng), Fn(from,to)))
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{
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}
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};
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``
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# Implement a holder class to hold the arguments required to construct the RangeAdaptor.
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The holder combines multiple parameters into one that can be passed as the right operand of `operator|()`.
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``
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template<typename T>
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class replace_holder : public boost::range_detail::holder2<T>
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{
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public:
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replace_holder(const T& from, const T& to)
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: boost::range_detail::holder2<T>(from, to)
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{ }
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private:
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void operator=(const replace_holder&);
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};
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``
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# Define an instance of the holder with the name of the adaptor
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``
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static boost::range_detail::forwarder2<replace_holder>
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replaced = boost::range_detail::forwarder2<replace_holder>();
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``
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# Define `operator|`
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``
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template<typename SinglePassRange>
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inline replace_range<SinglePassRange>
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operator|(SinglePassRange& rng,
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const replace_holder<typename boost::range_value<SinglePassRange>::type>& f)
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{
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return replace_range<SinglePassRange>(rng, f.val1, f.val2);
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}
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template<typename SinglePassRange>
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inline replace_range<const SinglePassRange>
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operator|(const SinglePassRange& rng,
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const replace_holder<typename boost::range_value<SinglePassRange>::type>& f)
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{
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return replace_range<const SinglePassRange>(rng, f.val1, f.val2);
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}
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``
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[endsect]
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[endsect]
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[endsect]
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