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deductiongu...ordered_map(3)   C++ Standard Libary  deductiongu...ordered_map(3)

NAME
     deductionguidesforstd::unordered_map - deductionguidesforstd::unordered_map

Synopsis
	Defined in header <unordered_map>
	template< class InputIt,

		  class Hash = std::hash<iter_key_t<InputIt>>,
		  class Pred = std::equal_to<iter_key_t<InputIt>>,
		  class Alloc =
	std::allocator<iter_to_alloc_t<InputIt>> >
	unordered_map( InputIt, InputIt,
		       typename /*see below*/::size_type = /*see     (1)  (since
     C++17)
	below*/,
		       Hash = Hash(), Pred = Pred(), Alloc = Alloc()
	)
	    -> unordered_map<iter_key_t<InputIt>,
	iter_val_t<InputIt>,

			     Hash, Pred, Alloc>;
	template< class Key, class T, class Hash = std::hash<Key>,

		  class Pred = std::equal_to<Key>,
		  class Alloc = std::allocator<std::pair<const Key,
	T>> >
	unordered_map( std::initializer_list<std::pair<Key, T>>,     (2)  (since
     C++17)
		       typename /*see below*/::size_type = /*see
	below*/,
		       Hash = Hash(), Pred = Pred(), Alloc = Alloc()
	)

	    -> unordered_map<Key, T, Hash, Pred, Alloc>;
	template< class InputIt, class Alloc >

	unordered_map( InputIt, InputIt, typename /*see
	below*/::size_type, Alloc )
	    -> unordered_map<iter_key_t<InputIt>,		     (3)  (since
     C++17)
	iter_val_t<InputIt>,
			     std::hash<iter_key_t<InputIt>>,

			     std::equal_to<iter_key_t<InputIt>>,
	Alloc>;
	template< class InputIt, class Alloc >

	unordered_map( InputIt, InputIt, Alloc )
	    -> unordered_map<iter_key_t<InputIt>,
	iter_val_t<InputIt>,					     (4)  (since
     C++17)
			     std::hash<iter_key_t<InputIt>>,

			     std::equal_to<iter_key_t<InputIt>>,
	Alloc>;
	template< class InputIt, class Hash, class Alloc >

	unordered_map( InputIt, InputIt, typename /*see
	below*/::size_type, Hash, Alloc )
	    -> unordered_map<iter_key_t<InputIt>,		     (5)  (since
     C++17)
	iter_val_t<InputIt>, Hash,

			     std::equal_to<iter_key_t<InputIt>>,
	Alloc>;
	template< class Key, class T, typename Alloc >

	unordered_map( std::initializer_list<std::pair<Key, T>>,
		       typename /*see below*/::size_type, Alloc )    (6)  (since
     C++17)

	    -> unordered_map<Key, T, std::hash<Key>,
	std::equal_to<Key>, Alloc>;
	template< class Key, class T, typename Alloc >

	unordered_map( std::initializer_list<std::pair<Key, T>>,
	Alloc ) 						     (7)  (since
     C++17)

	    -> unordered_map<Key, T, std::hash<Key>,
	std::equal_to<Key>, Alloc>;
	template< class Key, class T, class Hash, class Alloc >

	unordered_map( std::initializer_list<std::pair<Key, T>>,
		       typename /*see below*/::size_type, Hash,      (8)  (since
     C++17)
	Alloc )

	    -> unordered_map<Key, T, Hash, std::equal_to<Key>,
	Alloc>;
	template< ranges::input_range R,

		  class Hash = std::hash<range_key_t<R>>,
		  class Pred = std::equal_to<range_key_t<R>>,
		  class Alloc = std::allocator<range_to_alloc_t<R>>
	>
	unordered_map( std::from_range_t, R&&,			     (9)  (since
     C++23)
		       typename /* see description */::size_type =
	/* see description */,
		       Hash = Hash(), Pred = Pred(), Alloc = Alloc()
	)
	    -> unordered_map<range_key_t<R>, range_mapped_t<R>,

			     Hash, Pred, Alloc>;
	template< ranges::input_range R, class Alloc >

	unordered_map( std::from_range_t, R&&,
		       typename /* see description */::size_type,
	Alloc ) 						     (10) (since
     C++23)
	    -> unordered_map<range_key_t<R>, range_mapped_t<R>,
			     std::hash<range_key_t<R>>,

			     std::equal_to<range_key_t<R>>, Alloc>;
	template< ranges::input_range R, class Alloc >

	unordered_map( std::from_range_t, R&&, Alloc )
	    -> unordered_map<range_key_t<R>, range_mapped_t<R>,      (11) (since
     C++23)
			     std::hash<range_key_t<R>>,

			     std::equal_to<range_key_t<R>>, Alloc>;
	template< ranges::input_range R, class Hash, class Alloc >

	unordered_map( std::from_range_t, R&&, typename /* see
	description */::size_type,
		       Hash, Alloc )				     (12) (since
     C++23)
	    -> unordered_map<range_key_t<R>, range_mapped_t<R>,
	Hash,

			     std::equal_to<range_key_t<R>>, Alloc>;
	Exposition-only helper type aliases
	template< class InputIter >

	using iter_val_t =						  (expo-
     sition only*)

	    typename std::iterator_traits<InputIter>::value_type;
	template< class InputIter >

	using iter_key_t =						  (expo-
     sition only*)

	    std::remove_const_t< std::tuple_element_t<0,
	iter_val_t<InputIter>>>;
	template< class InputIter >

	using iter_mapped_t =						  (expo-
     sition only*)

	    std::tuple_element_t<1, iter_val_t<InputIter>>;
	template< class InputIter >

	using iter_to_alloc_t =
	    std::pair<std::add_const_t<tuple_element_t<0,		  (expo-
     sition only*)
	iter_val_t<InputIter>>>,

		      std::tuple_element_t<1,
	iter_val_t<InputIter>>>;
	template< ranges::input_range Range >

	using range_key_t =						  (since
     C++23)
									  (expo-
     sition only*)
	    std::remove_const_t<typename
	ranges::range_value_t<Range>::first_type>;
	template< ranges::input_range Range >
									  (since
     C++23)
	using range_mapped_t =						  (expo-
     sition only*)

	    typename ranges::range_value_t<Range>::second_type;
	template< ranges::input_range Range >

	using range_to_alloc_t =
	    std::pair<std::add_const_t<typename 			  (since
     C++23)
	ranges::range_value_t<Range>::first_type>,			  (expo-
     sition only*)

		      typename
	ranges::range_value_t<Range>::second_type>;

	1-8)  These  deduction guide are provided for unordered_map to allow de-
     duction from an
	iterator range (overloads (1,3-5)) and std::initializer_list  (overloads
     (2,6-8)).
	9-12) These deduction guides are provided for unordered_map to allow de-
     duction from
	a std::from_range_t tag and an input_range.

	These  overloads participate in overload resolution only if InputIt sat-
     isfies
	LegacyInputIterator, Alloc satisfies Allocator, neither  Hash  nor  Pred
     satisfy
	Allocator, and Hash is not an integral type.

	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.

	The size_type parameter type  in  these  guides  in  an  refers  to  the
     size_type member
	type of the type deduced by the deduction guide.

Notes
	    Feature-test macro	     Value    Std		    Feature
	__cpp_lib_containers_ranges  202202L  (C++23)  Ranges-aware construction
     and insertion;
						    overloads (9-12)

Example
     // Run this code

      #include <unordered_map>

      int main()
      {
	  // std::unordered_map m1 = {{"foo", 1}, {"bar", 2}};
	      // Error: braced-init-list has no type cannot
	      // deduce pair<Key, T> from {"foo", 1} or {"bar", 2}

	  std::unordered_map m1 = {std::pair{"foo", 2}, {"bar", 3}}; // guide #2
	  std::unordered_map m2(m1.begin(), m1.end()); // guide #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  3025  C++17       initializer-list  guides  take		     use
     std::pair<Key, T>
			    std::pair<const Key, T>

http://cppreference.com 	   2024.06.10	    deductiongu...ordered_map(3)
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