[ranges] Should constexpr default_sentinel_t end() be const-qualified? #5507
Description
The begin/end of basic_istream_view is defined in [range.istream.view]
template<movable Val, class CharT, class Traits = char_traits<CharT>>
class basic_istream_view : public view_interface<basic_istream_view<Val, CharT, Traits>> {
public:
constexpr auto begin() {
*stream_ >> value_;
return iterator{*this};
}
constexpr default_sentinel_t end() const noexcept;
};
Even if begin() is non-const-qualified, since end() simply returns default_sentinel, it is still designed to be const-qualified member function, which allows us to call as_const(r).end() even if as_const(r) is not a range.
However, the begin/end of chunk_view for input ranges is defined in [range.chunk.view.input] as
template<view V>
class chunk_view : public view_interface<chunk_view<V>> {
public:
constexpr outer-iterator begin();
constexpr default_sentinel_t end() noexcept;
};
Even though end() can be const-qualified, it is still designed to be non-const-qualified, which makes end()'s const-qualification consistent with begin()'s and prevents us from calling as_const(r).end().
Do we need to resolve this inconsistency?