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deductiongu...iority_queue(3) C++ Standard Libarydeductiongu...iority_queue(3)

NAME
       deductionguidesforstd::priority_queue  -	 deductionguidesforstd::prior-
       ity_queue

Synopsis
	  Defined in header <queue>
	  template <class Comp,	class Container>

	  priority_queue(Comp,					    Container)
       (1) (since C++17)

	  -> priority_queue<typename Container::value_type, Container,
	  Comp>;
	  template<class InputIt,

	  class	Comp = std::less</*iter-value-type*/<InputIt>>,
	  class	   Container	=    std::vector</*iter-value-type*/<InputIt>>
       (2) (since C++17)
	  priority_queue(InputIt, InputIt, Comp	= Comp(), Container =
	  Container())

	  -> priority_queue</*iter-value-type*/<InputIt>, Container, Comp>;
	  template<class Comp, class Container,	class Alloc>

	  priority_queue(Comp,		      Container,		Alloc)
       (3) (since C++17)

	  -> priority_queue<typename Container::value_type, Container,
	  Comp>;
	  template<class InputIt, class	Alloc>

	  priority_queue(InputIt, InputIt, Alloc)
	  ->			  priority_queue</*iter-value-type*/<InputIt>,
       (4) (since C++17)
	  std::vector</*iter-value-type*/<InputIt>, Alloc>,

	  std::less</*iter-value-type*/<InputIt>>>;
	  template<class InputIt, class	Comp, class Alloc>

	  priority_queue(InputIt,	 InputIt,	  Comp,		Alloc)
       (5) (since C++17)
	  -> priority_queue</*iter-value-type*/<InputIt>,

	  std::vector</*iter-value-type*/<InputIt>, Alloc>, Comp>;
	  template<class InputIt, class	Comp, class Container, class Alloc>

	  priority_queue(InputIt,    InputIt,	 Comp,	  Container,	Alloc)
       (6) (since C++17)

	  -> priority_queue<typename Container::value_type, Container,
	  Comp>;

	  These	deduction guides are provided for std::priority_queue to 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.

	  These	overloads participate in overload resolution only if

	    * InputIt satisfies	LegacyInputIterator,
	    * Comp does	not satisfy Allocator,
	    * Container	does not satisfy Allocator,
	    * for overloads (4)	and (5),
	      (since C++23) Alloc satisfies Allocator, and
	    * for overloads (3)	and (6), std::uses_allocator_v<Container,  Al-
       loc> is true.

	  Note:	 the  extent  to which the library determines that a type does
       not satisfy
	  LegacyInputIterator is unspecified, except that as a	minimum	 inte-
       gral types do not
	  qualify  as input iterators. Likewise, the extent to which it	deter-
       mines 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.

Example
       // Run this code

	#include <queue>
	#include <vector>
	#include <iostream>
	#include <functional>

	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::pri-
       ority_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 retroac-
       tively to
	  previously published C++ standards.

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

http://cppreference.com		  2022.07.31	 deductiongu...iority_queue(3)

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