3292. iota_view is under-constrained

Section: 25.6.4.2 [range.iota.view] Status: C++20 Submitter: Barry Revzin Opened: 2019-09-13 Last modified: 2021-02-25

Priority: Not Prioritized

View all other issues in [range.iota.view].

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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 25.6.4.2 [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> {
       […]
     };
     […]
   }