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

3578. Iterator SCARYness in the context of associative container merging

Section: [associative.reqmts.general] Status: New Submitter: Joaquín M López Muñoz Opened: 2021-08-04 Last modified: 2021-08-20

Priority: 3

View other active issues in [associative.reqmts.general].

View all other issues in [associative.reqmts.general].

View all issues with New status.


For the expression a.merge(a2), postconditions say that "iterators referring to the transferred elements […] now behave as iterators into a […]". When a and a2 are of different types, this seems to imply, under the widest interpretation for "behaving as", that a-iterators and a2-iterators are actually of the same type, that is, that associative containers have SCARY iterators, which is, to the best of my knowledge, not currently mandated by the standard.

There are (at least) three possible resolutions to this ambiguity, ordered by intrusiveness:

Note that this issue does not extend to unordered associative containers, as there ( [unord.req.general]) iterators to transferred elements are invalidated, which makes the point of SCARYness irrelevant. That said, if SCARY iterators are finally required for associative containers, it makes much sense to extend the requirement to unordered associative containers as well.

[2021-08-20; Reflector poll]

Set priority to 3 after reflector poll.

Proposed resolution: