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 (1) (since C++17)
   std::iterator_traits<InputIt>::value_type>>
   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>> (2) (since C++17)
   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>;
   template<class InputIt, class Alloc>
   unordered_set(InputIt, InputIt, typename /*see below*/::size_type,
   Alloc)
   -> unordered_set<typename (3) (since C++17)
   std::iterator_traits<InputIt>::value_type,
   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>,
   Allocator>;
   template<class T, class Allocator>
   unordered_set(std::initializer_list<T>, typename /*see (5) (since C++17)
   below*/::size_type, Allocator)
   -> 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 (6) (since C++17)
   below*/::size_type, Hash, Alloc)
   -> unordered_set<T, Hash, std::equal_to<T>, Alloc>;
   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
   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.

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