US294 24.07.10.3 p14,15 join_view::iterator::operator-- is improperly constrained LWG 3313

[wg21bot]

join_view::iterator::operator-- is improperly constrained. In the Effects clause in paragraph 14, we see the statement:

  inner_ = ranges::end(*--outer_);

However, this only well-formed when end returns an iterator, not a sentinel. This requirement is not reflected in the constraints of the function(s). 

Proposed change:
Change join_view::iterator::operator--() and operator--(int) to the following:

constexpr iterator& operator--()
requires ref_is_glvalue && bidirectional_range<Base> &&
bidirectional_range<range_reference_t<Base>> &&
common_range<range_reference_t<Base>>;

constexpr iterator operator--(int)
requires ref_is_glvalue && bidirectional_range<Base> &&
bidirectional_range<range_reference_t<Base>> &&
common_range<range_reference_t<Base>>;

[Dani-Hub]

The associated issue is LWG 3313

[JeffGarland]

Status to Ready during Tuesday morning issue processing in Belfast