As we all know, it is unreasonable to create basic_istream during compile-time. However, the member functions of basic_istream_view are all declared as constexpr. I don’t quite understand why?

If the intention here is to support constexpr basic_istream (which is not unreasonable), then why are almost all the members of basic_istream_view::iterator non-constexpr except for the constructor? I'm confused by such inconsistency.

Would it be more appropriate to remove all constexpr qualifiers from this section (although end() can be constexpr by its implementation)?

Did I miss something?