type_erased

#include <boost/range/adaptor/type_erased.hpp>
#include <boost/range/algorithm/copy.hpp>
#include <boost/assign.hpp>
#include <boost/foreach.hpp>
#include <iterator>
#include <iostream>
#include <list>
#include <vector>
// The client interface from an OO perspective merely requires a sequence
// of integers that can be forward traversed
typedef boost::any_range<
    int
  , boost::forward_traversal_tag
  , int
  , std::ptrdiff_t
> integer_range;
namespace server
{
    void display_integers(const integer_range& rng)
    {
        boost::copy(rng,
                    std::ostream_iterator<int>(std::cout, ","));
        std::cout << std::endl;
    }
}
namespace client
{
    void run()
    {
        using namespace boost::assign;
        using namespace boost::adaptors;
        // Under most conditions one would simply use an appropriate
        // any_range as a function parameter. The type_erased adaptor
        // is often superfluous. However because the type_erased
        // adaptor is applied to a range, we can use default template
        // arguments that are generated in conjunction with the
        // range type to which we are applying the adaptor.
        std::vector<int> input;
        input += 1,2,3,4,5;
        // Note that this call is to a non-template function
        server::display_integers(input);
        std::list<int> input2;
        input2 += 6,7,8,9,10;
        // Note that this call is to the same non-tempate function
        server::display_integers(input2);
        input2.clear();
        input2 += 11,12,13,14,15;
        // Calling using the adaptor looks like this:
        // Notice that here I have a type_erased that would be a
        // bidirectional_traversal_tag, but this is convertible
        // to the forward_traversal_tag equivalent hence this
        // works.
        server::display_integers(input2 | type_erased<>());
        // However we may simply wish to define an adaptor that
        // takes a range and makes it into an appropriate
        // forward_traversal any_range...
        typedef boost::adaptors::type_erased<
            boost::use_default
          , boost::forward_traversal_tag
        > type_erased_forward;
        // This adaptor can turn other containers with different
        // value_types and reference_types into the appropriate
        // any_range.
        server::display_integers(input2 | type_erased_forward());
    }
}
int main(int argc, const char* argv[])
{
    client::run();
    return 0;
}