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      deduction guides forstd::unordered_set

      From cppreference.com
      <cpp‎ |container‎ |unordered set

      [edit template]
       
       
       
      std::unordered_set
      Member types
      Member functions
      Non-member functions
      Deduction guides(C++17)
       
      Defined in header<unordered_set>
      template<

         class InputIt,
         class Hash=std::hash<typenamestd::iterator_traits<InputIt>::value_type>,
         class Pred=std::equal_to<typenamestd::iterator_traits<InputIt>::value_type>,
         class Alloc=std::allocator<typenamestd::iterator_traits<InputIt>::value_type>>
      unordered_set( InputIt, InputIt,
                     typename/* see below */::size_type=/* see below */,
                     Hash= Hash(), Pred= Pred(), Alloc= Alloc())
         -> unordered_set<typenamestd::iterator_traits<InputIt>::value_type,

                           Hash, Pred, Alloc>;
      		 (1)(since C++17)
      template<class T,

               class Hash=std::hash<T>,
               class Pred=std::equal_to<T>,
               class Alloc=std::allocator<T>>
      unordered_set(std::initializer_list<T>,
                     typename/* see below */::size_type=/* see below */,
                     Hash= Hash(), Pred= Pred(), Alloc= Alloc())

         -> unordered_set<T, Hash, Pred, Alloc>;
      		 (2)(since C++17)
      template<class InputIt,class Alloc>

      unordered_set( InputIt, InputIt,typename/* see below */::size_type, Alloc)
         -> unordered_set<typenamestd::iterator_traits<InputIt>::value_type,
                           std::hash<typenamestd::iterator_traits<InputIt>::value_type>,
                           std::equal_to<typenamestd::iterator_traits<InputIt>::value_type>,

                           Alloc>;
      		 (3)(since C++17)
      template<class InputIt,class Hash,class Alloc>

      unordered_set( InputIt, InputIt,typename/* see below */::size_type, Hash, Alloc)
         -> unordered_set<typenamestd::iterator_traits<InputIt>::value_type, Hash,
                           std::equal_to<typenamestd::iterator_traits<InputIt>::value_type>,

                           Alloc>;
      		 (4)(since C++17)
      template<class T,class Alloc>

      unordered_set(std::initializer_list<T>,typename/* see below */::size_type, Alloc)

         -> unordered_set<T,std::hash<T>,std::equal_to<T>, Alloc>;
      		 (5)(since C++17)
      template<class T,class Hash,class Alloc>

      unordered_set(std::initializer_list<T>,typename/* see below */::size_type,
                     Hash, Alloc)

         -> unordered_set<T, Hash,std::equal_to<T>, Alloc>;
      		 (6)(since C++17)
      template<ranges::input_range R,

               class Hash=std::hash<ranges::range_value_t<R>>,
               class Pred=std::equal_to<ranges::range_value_t<R>>,
               class Alloc=std::allocator<ranges::range_value_t<R>>>
      unordered_set(std::from_range_t, R&&,
                     typename/* see below */::size_type=/* see below */,
                     Hash= Hash(), Pred= Pred(), Alloc= Alloc())

         -> unordered_set<ranges::range_value_t<R>, Hash, Pred, Alloc>;
      		 (7)(since C++23)
      template<ranges::input_range R,class Alloc>

      unordered_set(std::from_range_t, R&&,
                     typename/* see below */::size_type, Alloc)
         -> unordered_set<ranges::range_value_t<R>, hash<ranges::range_value_t<R>>,

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

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

                           std::equal_to<ranges::range_value_t<R>>, Alloc>;
      		 (9)(since C++23)
      template<ranges::input_range R,class Hash,class Alloc>

      unordered_set(std::from_range_t, R&&,
                     typename/* see below */::size_type, Hash, Alloc)
         -> unordered_set<ranges::range_value_t<R>, Hash,

                           std::equal_to<ranges::range_value_t<R>>, Alloc>;
      		 (10)(since C++23)
      1-6) Thesededuction guides are provided forunordered_set to allow deduction from an iterator range (overloads(1,3,4)) andstd::initializer_list (overloads(2,5,6)). This overload participates in overload resolution only ifInputIt satisfiesLegacyInputIterator,Alloc satisfiesAllocator, neitherHash norPred satisfyAllocator,Hash is not an integral type.
      7-10) These deduction guides are provided forunordered_set to allow deduction from astd::from_range_t tag and aninput_range.

      Note: the extent to which the library determines that a type does not satisfyLegacyInputIterator 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 satisfyAllocator is unspecified, except that as a minimum the member typeAlloc::value_type must exist and the expressionstd::declval<Alloc&>().allocate(std::size_t{}) must be well-formed when treated as an unevaluated operand.

      Thesize_type parameter type in these guides refers to thesize_type member type of the type deduced by the deduction guide.

      [edit]Notes

      Feature-test macroValueStdFeature
      __cpp_lib_containers_ranges202202L(C++23)Ranges-aware construction and insertion; overloads(7-10)

      [edit]Example

      Run this code
      #include <unordered_set> int main(){// guide #2 deduces std::unordered_set<int>std::unordered_set s={1,2,3,4}; // guide #1 deduces std::unordered_set<int>std::unordered_set s2(s.begin(), s.end());}
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