Re: [Boost-users] [context] boost::coroutines::asymmetric_coroutine<T>::pull_type iterator does not properly model InputIterator

16 Feb 2015


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

#include 
#include 
#include 

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(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 
#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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Re: [Boost-users] [context] boost::coroutines::asymmetric_coroutine<T>::pull_type iterator does not properly model InputIterator

Oliver Kowalke