arximboldi
std::vector creation from immer::map/set iterator pair fails starting at gcc 14.3
The following fails to compile starting from gcc 14.3 (godbolt link):
#include <immer/map.hpp>
#include <unordered_map>
#include <vector>
int main()
{
auto um = std::unordered_map<int,int>{ {0,0}, {1,1}, {2,2} };
auto uv = std::vector<std::pair<int,int>>(um.begin(), um.end());
static_assert(!std::sized_sentinel_for<decltype(um.end()), decltype(um.begin())>);
auto im = immer::map<int,int>{ {0,0}, {1,1}, {2,2} };
auto iv = std::vector<std::pair<int,int>>(im.begin(), im.end());
static_assert(std::sized_sentinel_for<decltype(im.end()), decltype(im.begin())>);
return 0;
}
with the following:
/opt/compiler-explorer/gcc-14.3.0/include/c++/14.3.0/bits/ranges_base.h:961:23: required from 'constexpr std::iter_difference_t<typename std::decay<_Tp>::type> std::ranges::__distance_fn::operator()(_It&&, _Sent) const [with _It = immer::detail::hamts::champ_iterator<std::pair<int, int>, immer::map<int, int>::hash_key, immer::map<int, int>::equal_key, immer::memory_policy<immer::free_list_heap_policy<immer::cpp_heap>, immer::refcount_policy, immer::spinlock_policy>, 5>&; _Sent = immer::detail::hamts::champ_iterator<std::pair<int, int>, immer::map<int, int>::hash_key, immer::map<int, int>::equal_key, immer::memory_policy<immer::free_list_heap_policy<immer::cpp_heap>, immer::refcount_policy, immer::spinlock_policy>, 5>; std::iter_difference_t<typename std::decay<_Tp>::type> = long int; typename std::decay<_Tp>::type = immer::detail::hamts::champ_iterator<std::pair<int, int>, immer::map<int, int>::hash_key, immer::map<int, int>::equal_key, immer::memory_policy<immer::free_list_heap_policy<immer::cpp_heap>, immer::refcount_policy, immer::spinlock_policy>, 5>]'
961 | { return __last - static_cast<const decay_t<_It>&>(__first); }
| ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/opt/compiler-explorer/gcc-14.3.0/include/c++/14.3.0/bits/stl_vector.h:718:44: required from 'constexpr std::vector<_Tp, _Alloc>::vector(_InputIterator, _InputIterator, const allocator_type&) [with _InputIterator = immer::detail::hamts::champ_iterator<std::pair<int, int>, immer::map<int, int>::hash_key, immer::map<int, int>::equal_key, immer::memory_policy<immer::free_list_heap_policy<immer::cpp_heap>, immer::refcount_policy, immer::spinlock_policy>, 5>; <template-parameter-2-2> = void; _Tp = std::pair<int, int>; _Alloc = std::allocator<std::pair<int, int> >; allocator_type = std::allocator<std::pair<int, int> >]'
718 | = static_cast<size_type>(ranges::distance(__first, __last));
| ~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
<source>:12:67: required from here
12 | auto iv = std::vector<std::pair<int,int>>(im.begin(), im.end());
| ^
/opt/compiler-explorer/libs/immer/trunk/immer/detail/iterator_facade.hpp:172:23: error: static assertion failed
172 | static_assert(is_random_access, "");
but the equivalent code for a std::unordered_map works.
The problem might be that immer::map/set have iterator pairs for which std::sized_sentinel_for is satisfied. This then causes the wrong implementation of std::ranges::distance to be selected at compile time.
Note that both the iterators for std::unordered_map and immer::map are forward_iterator.
This is likely to affect many std::ranges::* function. For instance std::ranges::copy(im, iv) also fails to compile for the same reason.
I've found two possible solutions for this.
One is to modify iterator_facade.hpp such that all method / functions that use static_assert as "compile guard" are modified in order to use SFINAE, like so:
template <typename U = iterator_facade,
typename std::enable_if_t<U::is_random_access, bool> = true>
friend DifferenceTypeT operator-(const DerivedT& a, const DerivedT& b)
{
return access_t::distance_to(b, a);
}
Another solution would be to define std::disable_sized_sentinel_for conditioned on the proper C++ standard, adding the definition in champ_iterator.hpp, like so:
// IMMER_HAS_CPP20 defined as IMMER_HAS_CPP17 in config.hpp
#if IMMER_HAS_CPP20
namespace std {
template <typename T,
typename Hash,
typename Eq,
typename MP,
immer::detail::hamts::bits_t B>
inline constexpr bool disable_sized_sentinel_for<
immer::detail::hamts::champ_iterator<T, Hash, Eq, MP, B>,
immer::detail::hamts::champ_iterator<T, Hash, Eq, MP, B>> = true;
} // namespace std
#endif
See it work on godbolt.
Do you have a preference for either?
Edit: note that the doc states:
The disable_sized_sentinel_for variable template can be used to prevent iterators and sentinels that can be subtracted but do not actually model sized_sentinel_for from satisfying the concept.
which doesn't strike me as applicable for champ_iterator, as they can't be subtracted.