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boostorg / container

STL-like containers from Boost
http://www.boost.org/libs/container/
Boost Software License 1.0
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vec_iterator member typedef iterator_concept should only be defined in C++20 #195

Closed theodelrieu closed 2 years ago

theodelrieu commented 2 years ago

Hello,

After upgrading Boost to 1.77.0, I had compiler errors when trying to combine boost::container::flat_map and range-v3.

I'm using apple-clang 13, in C++17 mode.

vec_iterator added the following line, with no #ifdef around:

typedef std::contiguous_iterator_tag                                             iterator_concept;

Problem is that std::contiguous_iterator_tag is only defined in C++20, and it relies on a forward declaration found in boost/move/detail/iterator_traits.hpp (which is illegal IIRC).

Since range-v3 provides emulated concepts, it has to check the inheritence hierarchy of these tags, which requires them to be defined. As it makes use of iterator_concept the compiler is not happy:

/Users/theo/.conan/data/range-v3/0.11.0-r3/_/_/package/5ab84d6acfe1f23c4fae0ab88f26e3a396351ac9/include/concepts/concepts.hpp:878:13: error: incomplete type >'std::contiguous_iterator_tag' used in type trait expression
          META_IS_BASE_OF(U, T) &&
igaztanaga commented 2 years ago

I've tried to detect if the standard library defines std::contiguous_iterator_tag in commit before forward declaring it in the commit:

https://github.com/boostorg/move/commit/78f26da1f3a5a3831e9e70efe83f9c56eef94e8c

and then, following your suggestion, defined vec_iterator::iterator_concept when std::contiguous_iterator tag it's defined:

https://github.com/boostorg/container/commit/19e68ee05092ea3d107904a3d2b38a94494c62f5

Let me know if this fix helps with the issue.

igaztanaga commented 2 years ago

I've just checked that with the mentioned commits on Boost.Move and Boost.Container makes range-v3 happy with boost::container::vector in C++17 and C++20 modes.