boost::asymmetric_coroutine doesn't compile when used with boost::range::algorithms

[kozlov.taras@…]

I've tried to use generators produced by boost::asymmetric_coroutines together with boost::range::algorithms (for example find_if) and it fails to compile.

Following code raise compilation error

#include <boost/range/algorithm/count.hpp>
#include <boost/coroutine/all.hpp>

using namespace boost::range;
using namespace boost::coroutines;

asymmetric_coroutine<int>::pull_type make_dummy_range()
{
    return asymmetric_coroutine<int>::pull_type([](asymmetric_coroutine<int>::push_type& yield)
    {
        yield(1);
    });
}

template<typename Range>
void const_func(const Range& r)
{
    auto b = boost::begin(r);
}

int _tmain(int argc, _TCHAR* argv[])
{
    const_func(make_dummy_range());
	return 0;
}

c:\users\taras\documents\visual studio 2012\projects\coroutine_bug\coroutine_bug\coroutine_bug.cpp(23): error C2027: use of undefined type 'boost::coroutines::pull_coroutine<R>::const_iterator'
1>          with
1>          [
1>              R=int
1>          ]
1>          d:\work\3rdparty\boost_1_58_0\boost\coroutine\asymmetric_coroutine.hpp(812) : see declaration of 'boost::coroutines::pull_coroutine<R>::const_iterator'
1>          with
1>          [
1>              R=int
1>          ]
1>          c:\users\taras\documents\visual studio 2012\projects\coroutine_bug\coroutine_bug\coroutine_bug.cpp(28) : see reference to function template instantiation 'void const_func<boost::coroutines::pull_coroutine<R>>(const Range &)' being compiled
1>          with
1>          [
1>              R=int,
1>              Range=boost::coroutines::pull_coroutine<int>
1>          ]
1>c:\users\taras\documents\visual studio 2012\projects\coroutine_bug\coroutine_bug\coroutine_bug.cpp(23): error C2514: 'boost::coroutines::pull_coroutine<R>::const_iterator' : class has no constructors
1>          with
1>          [
1>              R=int
1>          ]
1>          d:\work\3rdparty\boost_1_58_0\boost\coroutine\asymmetric_coroutine.hpp(812) : see declaration of 'boost::coroutines::pull_coroutine<R>::const_iterator'
1>          with
1>          [
1>              R=int
1>          ]
1>
1>Build FAILED.

The problem is that boost::asymmetric_coroutine::const_iterator is declared but never defined, see boost/coroutine/asymmetric_coroutine.hpp:180

I detected this problem while was trying to migrate from Boost 1.55. With Boost 1.55 this code compiles and everything is fine.

[olli]

const_iterator must not be defined - it will never be const because each incrementation will modify/changed the associated coroutine. removing the declaration for const_iteration from the header will not help.

[kozlov.taras@…]

First of all boost coroutines and ranges can't be used together at the moment. This is definitly a bug. And ok, probably it should be fixed in Boost.Range

I want to clearify problem again. Using generator together with ANY non mutating Boost.Range algorithm yields compiler error

Example

asymmetric_coroutine<int>::pull_type make_dummy_range()
{
    return asymmetric_coroutine<int>::pull_type([](asymmetric_coroutine<int>::push_type& yield)
    {
        yield(1);
    });
}

int _tmain(int argc, _TCHAR* argv[])
{
    boost::for_each(make_dummy_range(), ...); //error
    boost::max_element(make_dummy_range()); //error
    boost::distance(make_dummy_range()); //error
    boost::find(make_dummy_range(), 1); //error
}

I put this bug to boost.coroutines for two reasons.

1. It is known problem that SinglePassRange can't define perfect const_iterator, but it is also common and convinient workaround to override range_const_iterator to return mutable iterator. So any algorithm which accept const Range& can work with it.

2. Coroutines in Boost 1.55 already provided const_iterator, so Boost 1.58 just broken some existing code.

[olli]

commit pushed to branch develop