id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
12071	Using iterator_facade with range-v3 fails to compile	Krzysztof Czaiński <1czajnik@…>	jeffrey.hellrung	"The fact that {{{postfix_increment_proxy}}} is not {{{DefaultConstructible}}} and doesn't have a nested public {{{value_type}}} makes iterators unusable with range-v3, which check the concepts.

Example:
{{{
#include ""boost/iterator/iterator_facade.hpp""
#include ""range/v3/utility/iterator.hpp""

template <class V, class Category>
class TestIter
    : public boost::iterator_facade<TestIter<V, Category>, V, Category, V> {
 public:
  using typename boost::iterator_facade<TestIter<V, Category>, V, Category,
                                        V>::difference_type;

  TestIter() : v_() {}

  explicit TestIter(V v) : v_(v) {}

 private:
  friend class boost::iterator_core_access;

  V dereference() const { return v_; }
  bool equal(const TestIter& other) const { return v_ == other.v_; }
  void increment() { ++v_; }
  void decrement() { --v_; }
  void advance(difference_type n) { v_ += n; }
  difference_type distance_to(const TestIter& other) const {
    return other.v_ - v_;
  }

  V v_;
};

using InIter = TestIter<int, std::input_iterator_tag>;

static_assert(ranges::InputIterator<InIter>(), """");

void f(InIter x) {
  static_assert(ranges::Readable<decltype(x++)>(), """");
  static_assert(ranges::DefaultConstructible<decltype(x++)>(), """");
}
}}}

I think {{{static_assert(ranges::InputIterator<InIter>(), """")}}} fails, because the two static_asserts in {{{f()}}} fail.

From what I've learned here:
https://github.com/ericniebler/range-v3/issues/304
it seems a good idea to fix {{{postfix_increment_proxy}}} to conform to these requirements. Ditto {{{writable_postfix_increment_proxy}}}."	Bugs	new	To Be Determined	iterator	Boost 1.61.0	Problem		range-v3