Title
std::array overview container requirements are incorrect
Status
new
Section
[array.overview][container.requirements.general]
Submitter
Nevin Liber & Christian Trott

Created on 2019-06-13.00:00:00, last changed 2019-07-23.15:26:26.

Messages

Date: 2019-07-23.15:26:26

Proposed resolution:

This wording is relative to N4810.

  1. Modify [container.requirements.general], Table 62 — "Container requirements", as indicated (This table can be identified by the "section" identifier [tab:container.req] in the next working draft):

    Table 62 — Container requirements
    Expression Return type Operational
    semantics
    Assertion/note
    pre/post-condition
    Complexity
    […]
    X u; Ensures: !u.empty() for array<T, N> where 0 < N, and
    Ensures: u.empty() for all other standard containers.
    constant(Note A)
    X() Ensures: !X().empty() for array<T, N> where 0 < N, and
    Ensures: X().empty() for all other standard containers.
    constant(Note A)
    […]

    Those entries marked "(Note A)" or "(Note B)" have linear complexity for array<T, N> where 0 < N and have constant complexity for all other standard containers.

  2. Modify [array.overview] as indicated:

    -2- An array is an aggregate ([dcl.init.aggr]) that can be list-initialized with up to N elements whose types are convertible to T.

    -3- An array<T, 0> satisfies all of the requirements of a container and of a reversible container ([container.requirements]). An array<T, N> where 0 < N satisfies all of the requirements of a container and of a reversible container ([container.requirements]), except that a default constructed array<T, N> object is not empty and thatboth default construction and swap does not have constantlinear complexity. An array satisfies some of the requirements of a sequence container ([sequence.reqmts]). Descriptions are provided here only for operations on array that are not described in one of these tables and for operations where there is additional semantic information.

Date: 2019-07-23.15:26:26

[ 2019-07 Issue Prioritiztion ]

Priority to 3 after discussion on the reflector.

Date: 2019-06-13.00:00:00

The requirements specified in [array.overview] p3 are incorrect; namely:

  • A default constructed array<T, N> where 0 < N has linear, not constant complexity.

  • A default constructed array<T, 0> is empty and has constant complexity.

History
Date User Action Args
2019-07-23 15:26:26adminsetmessages: + msg10501
2019-06-16 09:24:23adminsetmessages: + msg10446
2019-06-13 00:00:00admincreate