P0211 Allocator-aware library wrappers for dynamic allocation

[wg21bot]

P0211R2 Allocator-aware library wrappers for dynamic allocation (Thomas Köppe)

[jensmaurer]

LEWG-I in San Diego: Forward to LEWG for C++23.

[wg21bot]

P0211R3 Allocator-aware library wrappers for dynamic allocation (Thomas Köppe)

[brycelelbach]

Prague 2020-02 LEWG Minutes

P0211R3 std::allocate_unique

Chair: Bryce Adelstein Lelbach

Champion: Thomas Koeppe

Minute Taker: Ben Craig

Start Review: 2020-02-13 15:52

Should allocator_new/allocator_delete use allocator_traits<>::construct/allocator_traits<>::destroy instead of placement new/destroy?

Do we want allocator_new to take a T and rebind the allocator?

Start Polling: 16:20

POLL: We must have support for arrays in allocate_unique/allocator_new/allocator_delete in the first version we ship.

Strongly For	Weakly For	Neutral	Weakly Against	Strongly Against
0	0	12	4	0

Attendance:

# of Authors: 1

Author Position: N

POLL: Users should be able to name the types of the deleters returned by allocate_unique.

Strongly For	Weakly For	Neutral	Weakly Against	Strongly Against
1	6	3	2	0

Attendance: 33

# of Authors: 1

Author Position: WF

That has weak consensus.

POLL: We must have allocate_unique_for_overwrite in the first version we ship.

Strongly For	Weakly For	Neutral	Weakly Against	Strongly Against
0	5	9	1	0

Attendance: 33

# of Authors: 1

Author Position: N

That has weak consensus.

POLL: We must support cv-qualified types in the first version of allocate_unique/allocator_new/allocator_delete.

Strongly For	Weakly For	Neutral	Weakly Against	Strongly Against
1	9	2	1	0

Attendance: 33

# of Authors: 1

Author Position: SF

That has consensus.

What allocator should allocate_unique use in the allocator_deleter:

• The original allocator (e.g. A).
• The rebound allocator used for allocation (e.g. A::rebind<T>).
• The original allocator rebound to std::byte (reduces the number of allocator types you generate).
  • This breaks fancy pointer.

End: 16:53

CONSENSUS: Bring a revision of P0211R3 (allocator-aware library wrappers for dynamic allocation), with the guidance below, to LEWG for further review.

• Array support is not required right now.
• allocator_delete should be nameable by users.
• Bikeshed allocator_delete on the LEWG mailing list.
• allocate_unique/allocator_new/allocator_delete must support cv-qualified types.
• Add allocate_unique_for_overwrite.