#include <iostream>
#include <iterator>
#include <string>
#include <utility>

#include <boost/coroutine/all.hpp>
#include <boost/range/begin.hpp>
#include <boost/range/end.hpp>

template<typename Continuation>
void bar(Continuation && yield) {
      yield("Hello");
      yield(", ");
      yield("World");
      yield("!\n");
}

using T = std::string;
using coro_t = boost::coroutines::asymmetric_coroutine<T>;

coro_t::pull_type foo() {
      return coro_t::pull_type{
            [](coro_t::push_type& yield) {
                bar(std::forward<coro_t::push_type>(yield));
            }};
}

int main(int, char **) {
      auto f = foo();

      for ( auto i = boost::begin( f); i != boost::end( f); ++i) {
          std::cout << * i << std::endl;
      }

      return 0;
}

compiles with master branch

2015-02-16 9:22 GMT+01:00 Mueller-Roemer, Johannes Sebastian <Johannes.Sebastian.Mueller-Roemer@igd.fraunhofer.de>:

I’m currently on Boost 1.56 so this might have been fixed by now, but in a simple test Boost.Coroutine fails to properly model the InputIterator concept, because *it++ does not conform to the operational semantics { T tmp = *it; ++it; return tmp; } required by the standard.

 

The failing program:

 

#include <boost/coroutine/asymmetric_coroutine.hpp>

#include <iostream>

 

template<typename Continuation>

auto foo(Continuation && yield) -> void

{

      yield("Hello");

      yield(", ");

      yield("World");

      yield("!\n");

}

 

//using T = char const *;

using T = std::string;

 

auto foo() -> boost::coroutines::asymmetric_coroutine<T>::pull_type

{

      using namespace boost::coroutines;

      return asymmetric_coroutine<T>::pull_type{

            [](asymmetric_coroutine<T>::push_type& yield) { foo(yield); }

      };

}

 

auto main(int, char **) -> int

{

      auto f = foo();

      for(auto it = boost::begin(f); it != boost::end(f);)

            std::cout << *it++;

}

 

Which (on my machine) outputs:

, World!

X☺à      r2     ` ,     ` ,      Ç2      Ç

 

Failing to model the InputIterator concept is bad, because then it isn’t any kind of standards-conforming iterator at all. Interestingly, if T is char const * and not std::string the program works as expected. Is there some other subtle bug at work here?

 

--

Johannes S. Mueller-Roemer, MSc

Wiss. Mitarbeiter - Interactive Engineering Technologies (IET)

 

Fraunhofer-Institut für Graphische Datenverarbeitung IGD

Fraunhoferstr. 5  |  64283 Darmstadt  |  Germany

Tel +49 6151 155-606  |  Fax +49 6151 155-139

johannes.mueller-roemer@igd.fraunhofer.de  |  www.igd.fraunhofer.de

 


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