Proposed resolution:

This functionality is provided by P0083R3

[ 08-2016, Post-Chicago ]

Move to Tentatively Resolved

[ 2009-10 Santa Cruz: ]

Mark as NAD Future. No consensus to make the change at this time.

Original resolution [SUPERSEDED]:

In [associative.reqmts] Table 85, add:

Table 85 -- Associative container requirements (in addition to container)

Expression	Return type	Assertion/note pre-/post-condition	Complexity
a.erase(q)	...	...	...
a.extract(q)	pair<key_type, iterator>	Extracts the element pointed to by q and erases it from the set. Returns a pair containing the value pointed to by q and an iterator pointing to the element immediately following q prior to the element being erased. If no such element exists, returns a.end().	amortized constant

In [unord.req] Table 87, add:

Table 87 -- Unordered associative container requirements (in addition to container)

Expression	Return type	Assertion/note pre-/post-condition	Complexity
a.erase(q)	...	...	...
a.extract(q)	pair<key_type, iterator>	Extracts the element pointed to by q and erases it from the set. Returns a pair containing the value pointed to by q and an iterator pointing to the element immediately following q prior to the element being erased. If no such element exists, returns a.end().	amortized constant

[ 2009-09-20 Howard adds: ]

See the 2009-09-19 comment of 839 for an API which accomplishes this functionality and also addresses several other use cases which this proposal does not.

[ 2009-07 post-Frankfurt: ]

Leave Open. Alisdair to contact Chris Jefferson about this.

[ Post Summit Alisdair adds: ]

Would value_type be a better return type than key_type?

[ Summit: ]

We look forward to a paper on this topic. We recommend no action until a paper is available. The paper would need to address exception safety.

Addresses UK 239 [CD1]

It is not possible to take a move-only key out of an unordered container, such as (multi)set or (multi)map, or the new unordered containers.

Add below a.erase(q), a.extract(q), with the following notation:

a.extract(q)>, Return type pair<key, iterator> Extracts the element pointed to by q and erases it from the set. Returns a pair containing the value pointed to by q and an iterator pointing to the element immediately following q prior to the element being erased. If no such element exists,returns a.end().