std::begin and std::end are not overloaded for coroutine<>::pull_type

[robinjam]

The documentation says that std::begin and std::end are overloaded for coroutine<>::pull_type, but the following example code fails to compile on Clang (Xcode 11.4, macOS 10.15.4):

using namespace boost::coroutines2;

auto my_coro = coroutine<int>::pull_type{
    [](coroutine<int>::push_type& yield) {
        for (int i = 0; i < 5; ++i) {
            yield(i);
        }
    }
};

for (auto i = std::begin(my_coro); i != std::end(my_coro); ++i) {
// ^ No matching function for call to 'begin', No matching function for call to 'end'
    std::cout << *i << std::endl;
}

Calling detail::begin and detail::end directly works, and range-based for also works.

I'm not sure if this is a bug, a documentation problem, or a misunderstanding at my end.

[olk]

should be fixed with f3bf547 provide std::begin/std::end overloads for pull_coroutine