deductionguidesforstd::unordered_set(3)

NAME
deductionguidesforstd::unordered_set - deductionguidesforstd::unordered_set

Synopsis
   Defined in header <unordered_set>
   template<
       class InputIt,
       class Hash = std::hash<typename
   std::iterator_traits<InputIt>::value_type>,
       class Pred = std::equal_to<typename
   std::iterator_traits<InputIt>::value_type>,
       class Alloc = std::allocator<typename
   std::iterator_traits<InputIt>::value_type> > (1) (since C++17)
   unordered_set( InputIt, InputIt,
                  typename /* see below */::size_type = /* see below
   */,
                  Hash = Hash(), Pred = Pred(), Alloc = Alloc() )
       -> unordered_set<typename
   std::iterator_traits<InputIt>::value_type,
                        Hash, Pred, Alloc>;
   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>, (2) (since C++17)
                  typename /* see below */::size_type = /* see below
   */,
                  Hash = Hash(), Pred = Pred(), Alloc = Alloc() )
       -> unordered_set<T, Hash, Pred, Alloc>;
   template< class InputIt, class Alloc >
   unordered_set( InputIt, InputIt, typename /* see below
   */::size_type, Alloc )
       -> unordered_set<typename
   std::iterator_traits<InputIt>::value_type, (3) (since C++17)
                        std::hash<typename
   std::iterator_traits<InputIt>::value_type>,
                        std::equal_to<typename
   std::iterator_traits<InputIt>::value_type>,
                        Alloc>;
   template< class InputIt, class Hash, class Alloc >
   unordered_set( InputIt, InputIt, typename /* see below
   */::size_type, Hash, Alloc )
       -> unordered_set<typename (4) (since C++17)
   std::iterator_traits<InputIt>::value_type, Hash,
                        std::equal_to<typename
   std::iterator_traits<InputIt>::value_type>,
                        Alloc>;
   template< class T, class Alloc >
   unordered_set( std::initializer_list<T>, typename /* see below (5) (since C++17)
   */::size_type, Alloc )
       -> unordered_set<T, std::hash<T>, std::equal_to<T>, Alloc>;
   template< class T, class Hash, class Alloc >
   unordered_set( std::initializer_list<T>, typename /* see below
   */::size_type, (6) (since C++17)
                  Hash, Alloc )
       -> unordered_set<T, Hash, std::equal_to<T>, Alloc>;
   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&&, (7) (since C++23)
                  typename /* see below */::size_type = /* see below
   */,
                  Hash = Hash(), Pred = Pred(), Alloc = Alloc() )
       -> unordered_set<ranges::range_value_t<R>, Hash, Pred,
   Alloc>;
   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>, (8) (since C++23)
   hash<ranges::range_value_t<R>>,
                        std::equal_to<ranges::range_value_t<R>>,
   Alloc>;
   template< ranges::input_range R, class Alloc >
   unordered_set( std::from_range_t, R&&, Alloc )
       -> unordered_set<ranges::range_value_t<R>, (9) (since C++23)
   hash<ranges::range_value_t<R>>,
                        std::equal_to<ranges::range_value_t<R>>,
   Alloc>;
   template< ranges::input_range R, class Hash, class Alloc >
   unordered_set( std::from_range_t, R&&,
                  typename /* see below */::size_type, Hash, Alloc ) (10) (since C++23)
       -> unordered_set<ranges::range_value_t<R>, Hash,
                        std::equal_to<ranges::range_value_t<R>>,
   Alloc>;
   1-6) These deduction guides are provided for unordered_set to allow deduction from
   an iterator range (overloads (1,3,4)) and std::initializer_list (overloads (2,5,6)).
   This overload participates in overload resolution only if InputIt satisfies
   LegacyInputIterator, Alloc satisfies Allocator, neither Hash nor Pred satisfy
   Allocator, Hash is not an integral type.
   7-10) These deduction guides are provided for unordered_set to allow deduction from
   a std::from_range_t tag and an input_range.
   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 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 (7-10)

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());
 }