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### 3580. `iota_view's iterator`'s binary `operator+` should be improved

Section: 26.6.4.3 [range.iota.iterator] Status: WP Submitter: Zoe Carver Opened: 2021-08-14 Last modified: 2021-10-14

Priority: Not Prioritized

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Discussion:

`iota_view`'s iterator's `operator+` could avoid a copy construct by doing "`i += n; return i`" rather than "`return i += n;`" as seen in 26.6.4.3 [range.iota.iterator].

This is what libc++ has implemented and shipped, even though it may not technically be conforming (if a program asserted the number of copies, for example).

It might be good to update this operator and the minus operator accordingly.

[2021-08-20; Reflector poll]

Set status to Tentatively Ready after six votes in favour during reflector poll.

[2021-10-14 Approved at October 2021 virtual plenary. Status changed: Voting → WP.]

Proposed resolution:

This wording is relative to N4892.

1. Modify 26.6.4.3 [range.iota.iterator] as indicated:

   >     friend constexpr iterator operator+(iterator i, difference_type n)
   >       requires advanceable<W>;

   > > -20- Effects: Equivalent to:

   > > >     return i += n;
   > > >     return i;

   >     friend constexpr iterator operator+(difference_type n, iterator i)
   >       requires advanceable<W>;

   > > -21- Effects: Equivalent to: `return i + n;`

   >     friend constexpr iterator operator-(iterator i, difference_type n)
   >       requires advanceable<W>;

   > > -22- Effects: Equivalent to:

   > > >     return i -= n;
   > > >     return i;