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### 3292. `iota_view` is under-constrained

Section: 26.6.4.2 [range.iota.view] Status: C++20 Submitter: Barry Revzin Opened: 2019-09-13 Last modified: 2021-02-25

Priority: Not Prioritized

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Discussion:

P1207R4 changed `weakly_incrementable` from requiring `semiregular` to requiring `default_constructible && movable`.

`iota_view` currently is specified to require that `W` be just `weakly_incrementable`. But we have to copy the `W` from the view into its iterator and also in `operator*()` to return a `W`.

The shortest resolution is just to add "`&& semiregular<W>`" to the class constraints.

[Status to ready after discussion Friday morning in Belfast]

Proposed resolution:

This wording is relative to N4830.

1. Modify 26.6.4.2 [range.iota.view] as indicated:

   >     namespace std::ranges {
   >       […]
   >       template<weakly_incrementable W, semiregular Bound = unreachable_sentinel_t>
   >         requires weakly-equality-comparable-with<W, Bound> && semiregular<W>
   >       class iota_view : public view_interface<iota_view<W, Bound> {
   >         […]
   >       };
   >       […]
   >     }