Section: 24.2.2.5 [container.alloc.reqmts] Status: WP Submitter: jim x Opened: 2023-07-10 Last modified: 2023-11-22 16:02:17 UTC
Priority: Not Prioritized
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Discussion:
24.2.2.5 [container.alloc.reqmts] p2 says:
[…] an expression v of type T or const T, […]
Then 24.2.2.5 [container.alloc.reqmts] bullet (2.4) says:
T is Cpp17CopyInsertable into X means that, in addition to T being Cpp17MoveInsertable into X, the following expression is well-formed:
allocator_traits<A>::construct(m, p, v)
So, what is the value category of the expression v? We didn't explicitly phrase the wording. The intent may be that the value category of v is any defined value category in 7.2.1 [basic.lval], however, the intent is not clear in the current wording. Maybe, we can say:
[…] the following expression is well-formed:
allocator_traits<A>::construct(m, p, v)for v of any value category.
which can make the intent meaning clearer.
[2023-10-27; Reflector poll]
Set status to Tentatively Ready after five votes in favour during reflector poll.
[2023-11-11 Approved at November 2023 meeting in Kona. Status changed: Voting → WP.]
Proposed resolution:
This wording is relative to N4950.
Modify 24.2.2.5 [container.alloc.reqmts] as indicated:
-2- Given an allocator type A and given a container type X having a value_type identical to T and an allocator_type identical to allocator_traits<A>::rebind_alloc<T> and given an lvalue m of type A, a pointer p of type T*, an expression v that denotes an lvalue of type T or const T or an rvalue of type const T, and an rvalue rv of type T, the following terms are defined. […]
[…]
(2.3) — T is Cpp17MoveInsertable into X means that the following expression is well-formed:
allocator_traits<A>::construct(m, p, rv)and its evaluation causes the following postcondition to hold: The value of *p is equivalent to the value of rv before the evaluation.
[Note 1: rv remains a valid object. Its state is unspecified — end note](2.4) — T is Cpp17CopyInsertable into X means that, in addition to T being Cpp17MoveInsertable into X, the following expression is well-formed:
allocator_traits<A>::construct(m, p, v)and its evaluation causes the following postcondition to hold: The value of v is unchanged and is equivalent to *p.
[…]