deduction guides for std::unordered_set

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Containers library

Sequence

array (C++11)

vector

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

Views

span (C++20)

 

std::unordered_set

Member functions

unordered_set::unordered_set

unordered_set::~unordered_set

unordered_set::operator=

unordered_set::get_allocator

Iterators

unordered_set::beginunordered_set::cbegin

unordered_set::endunordered_set::cend

Capacity

unordered_set::empty

unordered_set::size

unordered_set::max_size

Modifiers

unordered_set::clear

unordered_set::insert

unordered_set::emplace

unordered_set::emplace_hint

unordered_set::erase

unordered_set::swap

unordered_set::extract (C++17)

unordered_set::merge (C++17)

Lookup

unordered_set::count

unordered_set::find

unordered_set::contains (C++20)

unordered_set::equal_range

Bucket interface

unordered_set::begin(size_type)unordered_set::cbegin(size_type)

unordered_set::end(size_type)unordered_set::cend(size_type)

unordered_set::bucket_count

unordered_set::max_bucket_count

unordered_set::bucket_size

unordered_set::bucket

Hash policy

unordered_set::load_factor

unordered_set::max_load_factor

unordered_set::rehash

unordered_set::reserve

Observers

unordered_set::hash_function

unordered_set::key_eq

Non-member functions

operator==operator!= (until C++20)

std::swap

erase_if (C++20)

Deduction guides(C++17)

 

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>, Allocator>;	(4)	(since C++17)
template<class T, class Allocator> unordered_set(std::initializer_list<T>, typename /*see below*/::size_type, Allocator)   -> 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)

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>
}