https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120305
--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> --- (In reply to aneris from comment #0) > The code compiles correctly if you replace all the long unsigned with just > unsigned though, which I find very peculiar, the code also compiles with > gnu++20 as the standard. An iota_view with unsigned elements (i.e. 32-bit integers) can use 64-bit integer for the difference_type of its iterators. An iota_view with unsigned long elements (i.e. 64-bit integers) must use something wider than 64 bits for the difference_type of its iterators. The C++20 standard allows that to be an integer type or an integer-like class type. In strict standard-conforming mode, we do not use the non-standard __int128 type for iota_view iterators, so we use an integer-like class type. The Cpp17InputIterator requirements do not allow an integer-like class type to be used, which means that in strict conformance mode, an iota_view with 64-bit elements has iterators which do not meet the Cpp17InputIterator requirements. You should not be assuming that C++20 ranges can be used in code that expects class STL-style iterators. C++20 iterators and classic STL-style iterators are not fully compatible with each other.
