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### 862. Impossible complexity for 'includes'

Section: 27.8.7.2 [includes] Status: NAD Editorial Submitter: Alisdair Meredith Opened: 2008-07-02 Last modified: 2016-01-28

Priority: Not Prioritized

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View all issues with NAD Editorial status.

Discussion:

In 27.8.7.2 [includes] the complexity is "at most -1 comparisons" if passed two empty ranges. I don't know how to perform a negative number of comparisions!

This same issue also applies to:

- `set_union`
- `set_intersection`
- `set_difference`
- `set_symmetric_difference`
- `merge`

[ 2009-03-30 Beman adds: ]

> Suggest NAD. The complexity of empty ranges is -1 in other places in the standard. See 27.8.6 [alg.merge] `merge` and `inplace_merge`, and `forward_list` merge, for example. The time and effort to find and fix all places in the standard where empty range[s] result in negative complexity isn't worth the very limited benefit.

[ 2009-05-09 Alisdair adds: ]

> I'm not happy with NAD if we can find a simple solution.

> How about adding a rider somewhere in clause 17 suggesting that complexities that specify a negative number of operations are treated as specifying zero operations? That should generically solve the issue without looking for further cases.

[ Batavia (2009-05): ]

> Pete to provide "straightforward" wording. Move to NAD Editorial.

Proposed resolution:

Recommend NAD.