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    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-val-t*/<InputIt>>, class Container = std::vector</*iter-val-t*/<InputIt> > priority_queue( InputIt, InputIt, Comp = Comp(), Container = Container() ) -> priority_queue</*iter-val-t*/<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-val-t*/<InputIt>, std::vector</*iter-val-t*/<InputIt>, Alloc>, std::less</*iter-val-t*/<InputIt>>>;
    		 (4) (since C++17)
    template< class InputIt, class Comp, class Alloc > priority_queue( InputIt, InputIt, Comp, Alloc ) -> priority_queue</*iter-val-t*/<InputIt>, std::vector</*iter-val-t*/<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)
    Exposition-only helper type aliases
    template< class InputIt > using /*iter-val-t*/ = typename std::iterator_traits<InputIt>::value_type;
    		 (exposition only*)
    See More

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

    1-6) Allow deduction from underlying container type and from an iterator range.
    7-9) Allow deduction from a std::from_range_t tag and an std::ranges::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, (4-6)