chapter 3 About boost::range

Concept

1. Range:

   • A concept similiar with STL container concept to fewer requirements.
   • Has 2 iterators that refer to the beginning and end of a group of elements that you can iterate over.

2. Range adaptor:

   • A class that wraps an existing Range to provide a new Range with different behaviour.
   • Provides iterators for accessing a half-open range [first,one_past_last) of elements.
   • Wraps the underlying iterators with new special iterators since the behaviour of Ranges is determined by their associated iterators.

3. Goal:

   • Range does not necessarily own the elements that can be accessed through it. (light)
   • Range object must be passed by reference in generic code. (performance)

4. Category:

   • Includes 4 types: Single pass range, Forward range, Bidirectional rangeand Random access range.
   • RandomAccessRng > BidirectionalRng > ForwardRng > SinglePassRng.

Adapter algorithm (Boost.Range):

• Expect a range as a first parameter, a container like std::vector can be passed directly.

• adjacent_filtered, copied, filtered, indexed, indirected, map_keys, map_values, replaced, replaced_if, reversed, sliced, strided, type_erased, tokenized, transformed and uniqued.

  • boost::map_values (Single Pass Range)

    #include <boost/range/adaptor/filtered.hpp>
    #include <boost/range/algorithm/copy.hpp>
    #include <boost/assign.hpp>
    #include <iterator>
    #include <iostream>
    #include <vector>
    
    using namespace boost::assign;
    using namespace boost::adaptors;
    int main(int argc, const char* argv[])
    {
        std::map<int,int> input;
        for (int i = 0; i < 10; ++i)
            input.insert(std::make_pair(i, i * 10));
    
        boost::copy(
            input | map_values,
            std::ostream_iterator<int>(std::cout, ","));
    
        return 0;
    }
    Output: 0,10,20,30,40,50,60,70,80,90,
    

  • boost::filtered (Forward Range)

    struct is_even {
        bool operator()( int x ) const { return x % 2 == 0; }
    };
    int main()
    {
        std::vector<int> input;
        input += 1,2,3,4,5,6,7,8,9;
        boost::copy(
            input | filtered(is_even()),
            std::ostream_iterator<int>(std::cout, ","));
        return 0;
    }
    Output: 2,4,6,8,
    

  • boost::reversed (Bidirectional Range)

    int main()
    {
        std::vector<int> input;
        input += 1,2,3,4,5,6,7,8,9;
        boost::copy(
            input | reversed,
            std::ostream_iterator<int>(std::cout, ","));
        return 0;
    }
    Output: 9,8,7,6,5,4,3,2,1,
    

  • boost::copied (Random Access Range)

    int main()
    {
      std::vector<int> input;
      input += 1,2,3,4,5,6,7,8,9,10;
      boost::copy(
          input | copied(1, 5),
          std::ostream_iterator<int>(std::cout, ","));
      return 0;
    }
    Output: 2,3,4,5,