deduction guides for std::unordered_map

 

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std::unordered_map

Member types
Member functions
unordered_map::unordered_map unordered_map::~unordered_map unordered_map::operator= unordered_map::get_allocator Iterators unordered_map::beginunordered_map::cbegin unordered_map::endunordered_map::cend Capacity unordered_map::size unordered_map::max_size unordered_map::empty Modifiers unordered_map::clear unordered_map::erase unordered_map::swap unordered_map::extract (C++17) unordered_map::merge (C++17) unordered_map::insert unordered_map::insert_range (C++23) unordered_map::insert_or_assign (C++17)   unordered_map::emplace unordered_map::emplace_hint unordered_map::try_emplace (C++17)	Lookup unordered_map::at unordered_map::operator[] unordered_map::count unordered_map::find unordered_map::contains (C++20) unordered_map::equal_range Bucket interface unordered_map::begin(size_type)unordered_map::cbegin(size_type) unordered_map::end(size_type)unordered_map::cend(size_type) unordered_map::bucket_count unordered_map::max_bucket_count unordered_map::bucket_size unordered_map::bucket Hash policy unordered_map::load_factor unordered_map::max_load_factor unordered_map::rehash unordered_map::reserve Observers unordered_map::hash_function unordered_map::key_eq
Non-member functions
operator==operator!= (until C++20)	std::swap(std::unordered_map) erase_if(std::unordered_map) (C++20)
Deduction guides(C++17)

 

Defined in header <unordered_map>
template<class InputIt,           class Hash =std::hash</*iter-key-t*/<InputIt>>,           class Pred =std::equal_to</*iter-key-t*/<InputIt>>,           class Alloc =std::allocator</*iter-to-alloc-t*/<InputIt>>> unordered_map( InputIt, InputIt,                typename/* see below */::size_type=/* see below */,                Hash = Hash(), Pred = Pred(), Alloc = Alloc())     -> unordered_map</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>,                      Hash, Pred, Alloc>;	(1)	(since C++17)
template<class Key, class T, class Hash =std::hash<Key>,           class Pred =std::equal_to<Key>,           class Alloc =std::allocator<std::pair<const Key, T>>> unordered_map(std::initializer_list<std::pair<Key, T>>,                typename/* see below */::size_type=/* see below */,                Hash = Hash(), Pred = Pred(), Alloc = Alloc())     -> unordered_map<Key, T, Hash, Pred, Alloc>;	(2)	(since C++17)
template<class InputIt, class Alloc > unordered_map( InputIt, InputIt, typename/* see below */::size_type, Alloc )     -> unordered_map</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>,                      std::hash</*iter-key-t*/<InputIt>>,                      std::equal_to</*iter-key-t*/<InputIt>>, Alloc>;	(3)	(since C++17)
template<class InputIt, class Alloc > unordered_map( InputIt, InputIt, Alloc )     -> unordered_map</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>,                      std::hash</*iter-key-t*/<InputIt>>,                      std::equal_to</*iter-key-t*/<InputIt>>, Alloc>;	(4)	(since C++17)
template<class InputIt, class Hash, class Alloc > unordered_map( InputIt, InputIt, typename/* see below */::size_type, Hash,                Alloc )     -> unordered_map</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>, Hash,                      std::equal_to</*iter-key-t*/<InputIt>>, Alloc>;	(5)	(since C++17)
template<class Key, class T, typename Alloc > unordered_map(std::initializer_list<std::pair<Key, T>>,                typename/* see below */::size_type, Alloc )     -> unordered_map<Key, T, std::hash<Key>, std::equal_to<Key>, Alloc>;	(6)	(since C++17)
template<class Key, class T, typename Alloc > unordered_map(std::initializer_list<std::pair<Key, T>>, Alloc )     -> unordered_map<Key, T, std::hash<Key>, std::equal_to<Key>, Alloc>;	(7)	(since C++17)
template<class Key, class T, class Hash, class Alloc > unordered_map(std::initializer_list<std::pair<Key, T>>,                typename/* see below */::size_type, Hash, Alloc )     -> unordered_map<Key, T, Hash, std::equal_to<Key>, Alloc>;	(8)	(since C++17)
template<ranges::input_range R,           class Hash =std::hash</*range-key-t*/<R>>,           class Pred =std::equal_to</*range-key-t*/<R>>,           class Alloc =std::allocator</*range-to-alloc-t*/<R>>> unordered_map(std::from_range_t, R&&,                typename/* see below */::size_type=/* see below */,                Hash = Hash(), Pred = Pred(), Alloc = Alloc())     -> unordered_map</*range-key-t*/<R>, /*range-mapped-t*/<R>,                      Hash, Pred, Alloc>;	(9)	(since C++23)
template<ranges::input_range R, class Alloc > unordered_map(std::from_range_t, R&&,                typename/* see below */::size_type, Alloc )     -> unordered_map</*range-key-t*/<R>, /*range-mapped-t*/<R>,                      std::hash</*range-key-t*/<R>>,                      std::equal_to</*range-key-t*/<R>>, Alloc>;	(10)	(since C++23)
template<ranges::input_range R, class Alloc > unordered_map(std::from_range_t, R&&, Alloc )     -> unordered_map</*range-key-t*/<R>, /*range-mapped-t*/<R>,                      std::hash</*range-key-t*/<R>>,                      std::equal_to</*range-key-t*/<R>>, Alloc>;	(11)	(since C++23)
template<ranges::input_range R, class Hash, class Alloc > unordered_map(std::from_range_t, R&&, typename/* see below */::size_type,                Hash, Alloc )     -> unordered_map</*range-key-t*/<R>, /*range-mapped-t*/<R>, Hash,                      std::equal_to</*range-key-t*/<R>>, Alloc>;	(12)	(since C++23)
Exposition-only helper type aliases
template<class InputIt > using/*iter-val-t*/=     typenamestd::iterator_traits<InputIt>::value_type;		(exposition only*)
template<class InputIt > using/*iter-key-t*/=     std::remove_const_t<std::tuple_element_t<0, /*iter-val-t*/<InputIt>>>;		(exposition only*)
template<class InputIt > using/*iter-mapped-t*/=     std::tuple_element_t<1, /*iter-val-t*/<InputIt>>;		(exposition only*)
template<class InputIt > using/*iter-to-alloc-t*/=     std::pair<std::add_const_t<tuple_element_t<0, /*iter-val-t*/<InputIt>>>,               std::tuple_element_t<1, /*iter-val-t*/<InputIt>>>;		(exposition only*)
template<ranges::input_range Range > using/*range-key-t*/=     std::remove_const_t<typenameranges::range_value_t<Range>::first_type>;		(since C++23) (exposition only*)
template<ranges::input_range Range > using/*range-mapped-t*/=     typenameranges::range_value_t<Range>::second_type;		(since C++23) (exposition only*)
template<ranges::input_range Range > using/*range-to-alloc-t*/=     std::pair<std::add_const_t<typenameranges::range_value_t<Range>::first_type>,               typenameranges::range_value_t<Range>::second_type>;		(since C++23) (exposition only*)

1-8) These deduction guide are provided for unordered_map to allow deduction from an iterator range (overloads (1,3-5)) and std::initializer_list (overloads (2,6-8)).

9-12) These deduction guides are provided for unordered_map to allow deduction from a std::from_range_t tag and an input_range.

These overloads participate in overload resolution only if InputIt satisfies LegacyInputIterator, Alloc satisfies Allocator, neither Hash nor Pred satisfy Allocator, and 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 in an 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 (9-12)

Example

Run this code

#include <unordered_map>   int main(){// std::unordered_map m1 = {{"foo", 1}, {"bar", 2}};// Error: braced-init-list has no type: cannot// deduce pair<Key, T> from {"foo", 1} or {"bar", 2}   std::unordered_map m1 ={std::pair{"foo", 2}, {"bar", 3}};// guide #2std::unordered_map m2(m1.begin(), m1.end());// guide #1}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 3025	C++17	initializer-list guides (2) and (6-8) take std::pair<const Key, T>	use std::pair<Key, T>