This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of Resolved status.

### 635. domain of `allocator::address`

Section: 16.4.4.6 [allocator.requirements] Status: Resolved Submitter: Howard Hinnant Opened: 2007-02-08 Last modified: 2016-01-28

Priority: Not Prioritized

View other active issues in [allocator.requirements].

View all other issues in [allocator.requirements].

View all issues with Resolved status.

Discussion:

The table of allocator requirements in 16.4.4.6 [allocator.requirements] describes `allocator::address` as:

>     a.address(r)
>     a.address(s)

where `r` and `s` are described as:

> a value of type `X::reference` obtained by the expression `*p`.

and `p` is

> a value of type `X::pointer`, obtained by calling `a1.allocate`, where `a1 == a`

This all implies that to get the address of some value of type `T` that value must have been allocated by this allocator or a copy of it.

However sometimes container code needs to compare the address of an external value of type `T` with an internal value. For example `list::remove(const T& t)` may want to compare the address of the external value `t` with that of a value stored within the list. Similarly `vector` or `deque insert` may want to make similar comparisons (to check for self-referencing calls).

Mandating that `allocator::address` can only be called for values which the allocator allocated seems overly restrictive.

[ post San Francisco: ]

> Pablo recommends NAD Editorial, solved by N2768.

[ 2009-04-28 Pablo adds: ]

> Tentatively-ready NAD Editorial as fixed by N2768.

[ 2009-07 Frankfurt ]

> Fixed by N2768.

[ 2009-07-28 Reopened by Alisdair. No longer solved by concepts. ]

[ 2009-10 Santa Cruz: ]

> NAD Editorial Resolved. Addressed by N2982.

Proposed resolution:

Change 16.4.4.6 [allocator.requirements]:

> `r` : a value of type `X::reference` obtained by the expression *p.

> `s` : a value of type `X::const_reference` obtained by the expression `*q` or by conversion from a value `r`.

[ post Oxford: This would be rendered NAD Editorial by acceptance of N2257. ]

[ Kona (2007): This issue is section 8 of N2387. There was some discussion of it but no resolution to this issue was recorded. Moved to Open. ]