Title
is_partitioned requirements need updating
Status
resolved
Section
[alg.partitions]
Submitter
Jonathan Wakely

Created on 2016-07-06.00:00:00 last changed 47 months ago

Messages

Date: 2020-05-12.16:49:02
Resolved by

Rationale:

P0896R4.
Date: 2020-05-15.00:00:00

[ 2020-05-12; Reflector discussions ]

Resolved by P0896R4.

Date: 2019-03-15.00:00:00

[ 2019-03-17; Daniel comments and removes previous wording ]

In the recent working draft N4810 all the "shall be convertible to Predicate's argument type" are gone - they were cleaned up when "The One Range" proposal P0896R4 had been accepted in San Diego 2018.

I also believe that we don't need the extra wording that was suggested in the previous P/R (effectively the need to say that the expression pred(*i) is well-formed), because this follows (in a more general way) by the expression invoke(pred, invoke(proj, e)) that is applied to the elements e of [first, last).

Therefore I'm suggesting that the resolution for this issue should be: Resolved by P0896R4.

Date: 2019-03-17.18:41:40

[ 2016-07, Toronto Saturday afternoon issues processing ]

The proposed resolution needs to be updated because the underlying wording has changed. Also, since the sequence is homogeneous, we shouldn't have to say that the expression is well-formed for all elements in the range; that implies that it need not be well-formed if the range is empty.

Marshall and JW to reword. Status to Open

Previous resolution [SUPERSEDED]:

This wording is relative to N4594.

  1. Edit [alg.partitions] as indicated:

    template <class InputIterator, class Predicate>
    bool is_partitioned(InputIterator first, InputIterator last, Predicate pred);
    

    -1- Requires: InputIterator's value type shall be convertible to Predicate's argument typeThe expression pred(*i) shall be well-formed for all i in [first, last).

    […]

    template <class InputIterator, class OutputIterator1,
              class OutputIterator2, class Predicate>
      pair<OutputIterator1, OutputIterator2>
      partition_copy(InputIterator first, InputIterator last,
                     OutputIterator1 out_true, OutputIterator2 out_false,
                     Predicate pred);
    

    -12- Requires: InputIterator's value type shall be CopyAssignable, and shall be writable ([iterator.requirements.general]) to the out_true and out_false OutputIterators, and shall be convertible to Predicate's argument typethe expression pred(*i) shall be well-formed for all i in [first, last). The input range shall not overlap with either of the output ranges.

    […]

    template<class ForwardIterator, class Predicate>
      ForwardIterator partition_point(ForwardIterator first,
                                      ForwardIterator last,
                                      Predicate pred);
    

    -16- Requires: ForwardIterator's value type shall be convertible to Predicate's argument typeThe expression pred(*i) shall be well-formed for all i in [first, last). [first, last) shall be partitioned by pred, i.e. all elements that satisfy pred shall appear before those that do not.

    […]

Date: 2016-07-06.00:00:00

Requires: InputIterator's value type shall be convertible to Predicate's argument type.

This seems to date from the days of adaptable function objects with an argument_type typedef, but in modern C++ the predicate might not have an argument type. It could have a function template that accepts various arguments, so it doesn't make sense to state requirements in terms of a type that isn't well defined.

History
Date User Action Args
2020-05-12 16:49:02adminsetmessages: + msg11293
2020-05-12 16:49:02adminsetmessages: + msg11292
2020-05-12 16:49:02adminsetstatus: open -> resolved
2017-07-16 20:43:29adminsetmessages: + msg9420
2017-07-16 20:43:29adminsetstatus: new -> open
2016-07-10 13:47:02adminsetmessages: + msg8240
2016-07-06 00:00:00admincreate