deduction guides for std::priority_queue

From cppreference.com
C++
Containers library
std::priority_queue
Defined in header <queue>
template < class Comp, class Container >

priority_queue ( Comp, Container )

- > priority_queue < typename Container :: value_type , Container, Comp > ;
(1) (since C++17)
template < class InputIt,

class Comp = std:: less < /*iter-value-type*/ < InputIt >> ,
class Container = std:: vector < /*iter-value-type*/ < InputIt > >
priority_queue ( InputIt, InputIt, Comp = Comp ( ) , Container = Container ( ) )

- > priority_queue < /*iter-value-type*/ < InputIt > , Container, Comp > ;
(2) (since C++17)
template < class Comp, class Container, class Alloc >

priority_queue ( Comp, Container, Alloc )

- > priority_queue < typename Container :: value_type , Container, Comp > ;
(3) (since C++17)
template < class InputIt, class Alloc >

priority_queue ( InputIt, InputIt, Alloc )
- > priority_queue < /*iter-value-type*/ < InputIt > ,
std:: vector < /*iter-value-type*/ < InputIt > , Alloc > ,

std:: less < /*iter-value-type*/ < InputIt >>> ;
(4) (since C++17)
template < class InputIt, class Comp, class Alloc >

priority_queue ( InputIt, InputIt, Comp, Alloc )
- > priority_queue < /*iter-value-type*/ < InputIt > ,

std:: vector < /*iter-value-type*/ < InputIt > , Alloc > , Comp > ;
(5) (since C++17)
template < class InputIt, class Comp, class Container, class Alloc >

priority_queue ( InputIt, InputIt, Comp, Container, Alloc )

- > priority_queue < typename Container :: value_type , Container, Comp > ;
(6) (since C++17)
template < ranges:: input_range R,

class Comp = std:: less < ranges:: range_value_t < R >> >
priority_queue ( std:: from_range_t , R && , Comp = Comp ( ) )
- > priority_queue < ranges:: range_value_t < R > ,

std:: vector < ranges:: range_value_t < R >> , Comp > ;
(7) (since C++23)
template < ranges:: input_range R, class Comp, class Alloc >

priority_queue ( std:: from_range_t , R && , Comp, Alloc )
- > priority_queue < ranges:: range_value_t < R > ,

std:: vector < ranges:: range_value_t < R > , Alloc > , Comp > ;
(8) (since C++23)
template < ranges:: input_range R, class Alloc >

priority_queue ( std:: from_range_t , R && , Alloc )
- > priority_queue < ranges:: range_value_t < R > ,

std:: vector < ranges:: range_value_t < R > , Alloc >> ;
(9) (since C++23)

The following deduction guides are provided for std::priority_queue :

1-6) Allow deduction from underlying container type and from an iterator range. /*iter-value-type*/ < It > denotes typename std:: iterator_traits < It > :: value_type for any type It .
7-9) Allow deduction from a std::from_range_t tag and an input_range .

These overloads participate in overload resolution only if

Note: the extent to which the library determines that a type does not satisfy LegacyInputIterator is unspecified, except that as a minimum integral types do not qualify as input iterators. Likewise, the extent to which it determines that a type does not satisfy Allocator is unspecified, except that as a minimum the member type Alloc::value_type must exist and the expression std:: declval < Alloc & > ( ) . allocate ( std:: size_t { } ) must be well-formed when treated as an unevaluated operand.

Notes

Feature-test macro Value Std Feature
__cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construction and insertion; overloads (7-9)

Example

Run this code 
#include <functional>
#include <iostream>
#include <queue>
#include <vector>
 
int main()
{
    const std::vector<int> v = {1, 2, 3, 4};
    std::priority_queue pq1{std::greater<int>{}, v}; // deduces std::priority_queue<
                                                     //     int, std::vector<int>,
                                                     //     std::greater<int>>
    for (; !pq1.empty(); pq1.pop())
        std::cout << pq1.top() << ' ';
    std::cout << '\n';
 
    std::priority_queue pq2{v.begin(), v.end()}; // deduces std::priority_queue<int>
 
    for (; !pq2.empty(); pq2.pop())
        std::cout << pq2.top() << ' ';
    std::cout << '\n';
}

Output: 

1 2 3 4
4 3 2 1

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3506 C++17 deduction guides from iterator and allocator were missing added
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