3447. Deduction guides for take_view and drop_view have different constraints

Section: 25.7.10.2 [range.take.view] Status: C++23 Submitter: Jens Maurer Opened: 2020-05-15 Last modified: 2023-11-22

Priority: 0

View all other issues in [range.take.view].

View all issues with C++23 status.

Discussion:

From this editorial issue request:

(Note "range R" vs "class R".)

In 25.7.10.2 [range.take.view], the deduction guide for take_view is declared as:

template<range R>
  take_view(R&&, range_difference_t<R>)
    -> take_view<views::all_t<R>>;

In 25.7.12.2 [range.drop.view], the deduction guide for drop_view is declared as:

template<class R>
  drop_view(R&&, range_difference_t<R>) -> drop_view<views::all_t<R>>;

Note the difference between their template parameter lists.

Suggested resolution:

Change the deduction guide of take_view from

template<range R>

to

template<class R>

[2020-07-17; Moved to Ready in telecon]

[2020-11-09 Approved In November virtual meeting. Status changed: Ready → WP.]

Proposed resolution:

This wording is relative to N4861.

1. Modify 25.7.10.2 [range.take.view], class template take_view synopsis, as indicated:

   […]
   template<rangeclass R>
     take_view(R&&, range_difference_t<R>)
       -> take_view<views::all_t<R>>;
   […]