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  1. #include <iostream>
  2. #include <string>
  3. #include <boost/shared_ptr.hpp>
  4. #include <boost/make_shared.hpp>
  5. #include <boost/bimap.hpp>
  6. #include <boost/iterator/transform_iterator.hpp>
  7.  
  8. struct A
  9. {
  10.     std::string data;
  11.     A(const std::string& s) : data(s) {}
  12. };
  13.  
  14. typedef boost::bimap<unsigned int, boost::shared_ptr<A> > container_type;
  15. typedef container_type::left_map::const_iterator base_const_iterator;
  16.  
  17. template <typename T>
  18. struct makeIterConst : std::unary_function<base_const_iterator::value_type const &,
  19.                                            std::pair<unsigned int const, boost::shared_ptr<T const> const> >
  20. {
  21.      std::pair<unsigned int const, boost::shared_ptr<T const> const> operator()
  22.              (base_const_iterator::value_type const & orig) const
  23.      {
  24.          std::pair<int const, boost::shared_ptr<T const> const> newPair(orig.first, boost::const_pointer_cast<T const>(orig.second));
  25.          return newPair;
  26.      }
  27. };
  28.  
  29. typedef boost::transform_iterator<makeIterConst<A>,
  30.                                  base_const_iterator> const_iterator;
  31.  
  32. int main()
  33. {
  34.     container_type m;
  35.     boost::shared_ptr<A> p = boost::make_shared<A>("foo");
  36.     m.insert( container_type::value_type(1, p));
  37.  
  38.     //  using regular iterator
  39.     for( base_const_iterator left_iter  = m.left.begin();
  40.                              left_iter != m.left.end();
  41.                            ++left_iter )
  42.     {
  43.         std::cout << left_iter->first << " --> " << left_iter->second->data << '\n';
  44.         left_iter->second->data =  "bar"; // compiles
  45.     }
  46.  
  47.     // using constified iterator
  48.     for( const_iterator left_iter  = boost::make_transform_iterator(m.left.begin(), makeIterConst<A>() );
  49.                         left_iter != boost::make_transform_iterator(m.left.end(), makeIterConst<A>() );
  50.                       ++left_iter )
  51.     {
  52.         std::cout << left_iter->first << " --> " << left_iter->second->data << '\n';
  53. //   the following will give a compilation error, as expected
  54. //      left_iter->second->data =  "changed_foo";
  55.     }
  56. }
  57.  
Success #stdin #stdout 0s 2868KB
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stdin
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Standard input is empty
stdout
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1 --> foo
1 --> bar
https://ideone.com/fHIUe
language:
C++ (gcc 8.3)
created:
13 years ago
visibility:
public

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