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### 3189. Missing requirement for `std::priority_queue`

Section: 22.6.5 [priority.queue] Status: New Submitter: Jonathan Wakely Opened: 2019-02-21 Last modified: 2019-03-05

Priority: 3

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Discussion:

We don't require that the `Compare` template parameter can be invoked with arguments of the queue's value type. It seems like something we can use Mandates: for, since it'll be ill-formed otherwise. Something like `is_invocable_r_v<bool, Compare&, value_type&, value_type&>`.

This might also apply to the `Compare` parameter for the `merge` and `sort` functions of `forward_list` and `list`.

[2019-03-05 Priority set to 3 after reflector discussion]

Proposed resolution: