Proposed resolution:

This wording is relative to N4878.

1. Add the following paragraph at the end of [container.adaptors.general]:

   -6- The exposition-only alias template iter-value-type defined in [sequences.general] may appear in deduction guides for container adaptors.

2. Modify [priority.queue], class template priority_queue synopsis, as indicated:

   namespace std {
     template<class T, class Container = vector<T>,
               class Compare = less<typename Container::value_type>>
     class priority_queue {
   
     // […]
   
     public:
       priority_queue() : priority_queue(Compare()) {}
       explicit priority_queue(const Compare& x) : priority_queue(x, Container()) {}
       priority_queue(const Compare& x, const Container&);
       priority_queue(const Compare& x, Container&&);
       template<class InputIterator>
         priority_queue(InputIterator first, InputIterator last, const Compare& x,
                         const Container&);
       template<class InputIterator>
         priority_queue(InputIterator first, InputIterator last,
                         const Compare& x = Compare(), Container&& = Container());
       template<class Alloc> explicit priority_queue(const Alloc&);
       template<class Alloc> priority_queue(const Compare&, const Alloc&);
       template<class Alloc> priority_queue(const Compare&, const Container&, const Alloc&);
       template<class Alloc> priority_queue(const Compare&, Container&&, const Alloc&);
       template<class Alloc> priority_queue(const priority_queue&, const Alloc&);
       template<class Alloc> priority_queue(priority_queue&&, const Alloc&);
       template<class InputIterator, class Alloc>
         priority_queue(InputIterator, InputIterator, const Alloc&);
       template<class InputIterator, class Alloc>
         priority_queue(InputIterator, InputIterator, const Compare&, const Alloc&);
       template<class InputIterator, class Alloc>
         priority_queue(InputIterator, InputIterator, const Compare&, const Container&, const Alloc&);
       template<class InputIterator, class Alloc>
         priority_queue(InputIterator, InputIterator, const Compare&, Container&&, const Alloc&);
   
     // […]
   
     };
   
     template<class Compare, class Container>
       priority_queue(Compare, Container)
         -> priority_queue<typename Container::value_type, Container, Compare>;
   
     template<class InputIterator,
               class Compare = less<typename iterator_traitsiter-value-type<InputIterator>::value_type>,
               class Container = vector<typename iterator_traitsiter-value-type<InputIterator>::value_type>>
       priority_queue(InputIterator, InputIterator, Compare = Compare(), Container = Container())
         -> priority_queue<typename iterator_traitsiter-value-type<InputIterator>::value_type, Container, Compare>;
   
     template<class Compare, class Container, class Allocator>
       priority_queue(Compare, Container, Allocator)
         -> priority_queue<typename Container::value_type, Container, Compare>;
   
     template<class InputIterator, class Allocator>
       priority_queue(InputIterator, InputIterator, Allocator)
         -> priority_queue<iter-value-type<InputIterator>,
                           vector<iter-value-type<InputIterator>, Allocator>,
                           less<iter-value-type<InputIterator>>>;
   
     template<class InputIterator, class Compare, class Allocator>
       priority_queue(InputIterator, InputIterator, Compare, Allocator)
         -> priority_queue<iter-value-type<InputIterator>,
                           vector<iter-value-type<InputIterator>, Allocator>, Compare>;
   
     template<class InputIterator, class Compare, class Container, class Allocator>
       priority_queue(InputIterator, InputIterator, Compare, Container, Allocator)
         -> priority_queue<typename Container::value_type, Container, Compare>;
   
     // […]
   }
   

3. Add the following paragraphs to [priqueue.cons.alloc]:

   template<class InputIterator, class Alloc>
     priority_queue(InputIterator first, InputIterator last, const Alloc& a);
   

   -?- Effects: Initializes c with first as the first argument, last as the second argument, and a as the third argument, and value-initializes comp; calls make_heap(c.begin(), c.end(), comp).

   template<class InputIterator, class Alloc>
     priority_queue(InputIterator first, InputIterator last, const Compare& compare, const Alloc& a);
   

   -?- Effects: Initializes c with first as the first argument, last as the second argument, and a as the third argument, and initializes comp with compare; calls make_heap(c.begin(), c.end(), comp).

   template<class InputIterator, class Alloc>
     priority_queue(InputIterator first, InputIterator last, const Compare& compare, const Container& cont, const Alloc& a);
   

   -?- Effects: Initializes c with cont as the first argument and a as the second argument, and initializes comp with compare; calls c.insert(c.end(), first, last); and finally calls make_­heap(c.begin(), c.end(), comp).

   template<class InputIterator, class Alloc>
     priority_queue(InputIterator first, InputIterator last, const Compare& compare, Container&& cont, const Alloc& a);
   

   -?- Effects: Initializes c with std::move(cont) as the first argument and a as the second argument, and initializes comp with compare; calls c.insert(c.end(), first, last); and finally calls make_­heap(c.begin(), c.end(), comp).

[ 2021-06-07 Approved at June 2021 virtual plenary. Status changed: Voting → WP. ]

[ 2021-02-26; LWG telecon ]

Set status to Tentatively Ready after discussion and poll.

[ 2021-02-17 Tim adds PR ]

[ 2020-11-29; Reflector prioritization ]

Set priority to 3 during reflector discussions. It has been pointed out that this issue is related to LWG 1199, LWG 2210, and LWG 2713.

priority_queue has two constructor templates taking a pair of input iterators in addition to a comparator and a container, but it does not have allocator-extended constructors corresponding to these constructor templates:

template<class InputIterator>
  priority_queue(InputIterator first, InputIterator last, const Compare& x,
                 const Container&);
template<class InputIterator>
  priority_queue(InputIterator first, InputIterator last,
                 const Compare& x = Compare(), Container&& = Container());