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### 3567. Formatting move-only iterators take two

Section: 22.14.6.6 [format.context] Status: WP Submitter: Casey Carter Opened: 2021-06-08 Last modified: 2021-10-14

Priority: Not Prioritized

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Discussion:

LWG 3539 fixed copies of potentially-move-only iterators in the `format_to` and `vformat_to` overloads, but missed the fact that member functions of `basic_format_context` are specified to copy iterators as well. In particular, 22.14.6.6 [format.context] states:

>     iterator out();

> > -7- Returns: `out_`.

>     void advance_to(iterator it);

> > -8- Effects: Equivalent to: `out_ = it;`

both of which appear to require copyability.

[2021-06-23; 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 N4885.

1. Modify 22.14.6.6 [format.context] as indicated:

   >     iterator out();

   > > -7- Returns: `out_`.Effects: Equivalent to: `return std::move(out_);`

   >     void advance_to(iterator it);

   > > -8- Effects: Equivalent to: `out_ = std::move(it);`