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deduction guides for std::unordered_set

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> >
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>;
 (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<typename 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>;
 (3) (since C++17) 
template< class InputIt, class Hash, class Alloc >
unordered_set( InputIt, InputIt, typename /* see below */::size_type, Hash, Alloc )
    -> unordered_set<typename std::iterator_traits<InputIt>::value_type, Hash,
                     std::equal_to<typename std::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) 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

#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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