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deduction guides for 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

#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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