Home Original page

deduction guides for std::unordered_multimap - cppreference.com

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_multimap( InputIt, InputIt, {{#pad:|18}} typename /* see below */::size_type = /* see below */, {{#pad:|18}} Hash = Hash(), Pred = Pred(), Alloc = Alloc() ) -> unordered_multimap</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>, {{#pad:|18}} 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_multimap( std::initializer_list<std::pair<Key, T>>, {{#pad:|18}} typename /* see below */::size_type = /* see below */, {{#pad:|18}} Hash = Hash(), Pred = Pred(), Alloc = Alloc() ) -> unordered_multimap<Key, T, Hash, Pred, Alloc>;

 (2) (since C++17)

template< class InputIt, class Alloc > unordered_multimap( InputIt, InputIt, typename /* see below */::size_type, Alloc ) -> unordered_multimap</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>, {{#pad:|18}} std::hash</*iter-key-t*/<InputIt>>, {{#pad:|18}} std::equal_to</*iter-key-t*/<InputIt>>, Alloc>;

 (3) (since C++17)

template< class InputIt, class Alloc > unordered_multimap( InputIt, InputIt, Alloc ) -> unordered_multimap</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>, {{#pad:|18}} std::hash</*iter-key-t*/<InputIt>>, {{#pad:|18}} std::equal_to</*iter-key-t*/<InputIt>>, Alloc>;

 (4) (since C++17)

template< class InputIt, class Hash, class Alloc > unordered_multimap( InputIt, InputIt, typename /* see below */::size_type, Hash, {{#pad:|18}} Alloc ) -> unordered_multimap</*iter-key-t*/<InputIt>, /*iter-val-t*/<InputIt>, Hash, {{#pad:|18}} std::equal_to</*iter-key-t*/<InputIt>>, Alloc>;

 (5) (since C++17)

template< class Key, class T, typename Alloc > unordered_multimap( std::initializer_list<std::pair<Key, T>>, {{#pad:|18}} typename /* see below */::size_type, Alloc ) -> unordered_multimap<Key, T, std::hash<Key>, std::equal_to<Key>, Alloc>;

 (6) (since C++17)

template< class Key, class T, typename Alloc > unordered_multimap( std::initializer_list<std::pair<Key, T>>, Alloc ) -> unordered_multimap<Key, T, std::hash<Key>, std::equal_to<Key>, Alloc>;

 (7) (since C++17)

template< class Key, class T, class Hash, class Alloc > unordered_multimap( std::initializer_list<std::pair<Key, T>>, {{#pad:|18}} typename /* see below */::size_type, Hash, Alloc ) -> unordered_multimap<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_multimap( std::from_range_t, R&&, {{#pad:|18}} typename /* see below */::size_type = /* see below */, {{#pad:|18}} Hash = Hash(), Pred = Pred(), Alloc = Alloc() ) -> unordered_multimap</*range-key-t*/<R>, /*range-mapped-t*/<R>, {{#pad:|18}} Hash, Pred, Alloc>;

 (9) (since C++23)

template< ranges::input_range R, class Alloc > unordered_multimap( std::from_range_t, R&&, {{#pad:|18}} typename /* see below */::size_type, Alloc ) -> unordered_multimap</*range-key-t*/<R>, /*range-mapped-t*/<R>, {{#pad:|18}} std::hash</*range-key-t*/<R>>, {{#pad:|18}} std::equal_to</*range-key-t*/<R>>, Alloc>;

 (10) (since C++23)

template< ranges::input_range R, class Alloc > unordered_multimap( std::from_range_t, R&&, Alloc ) -> unordered_multimap</*range-key-t*/<R>, /*range-mapped-t*/<R>, {{#pad:|18}} std::hash</*range-key-t*/<R>>, {{#pad:|18}} std::equal_to</*range-key-t*/<R>>, Alloc>;

 (11) (since C++23)

template< ranges::input_range R, class Hash, class Alloc > unordered_multimap( std::from_range_t, R&&, typename /* see below */::size_type, {{#pad:|18}} Hash, Alloc ) -> unordered_multimap</*range-key-t*/<R>, /*range-mapped-t*/<R>, Hash, {{#pad:|18}} std::equal_to</*range-key-t*/<R>>, Alloc>;

 (12) (since C++23)

Exposition-only helper type aliases

template< class InputIt > using /*iter-val-t*/ = typename std::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<typename ranges::range_value_t<Range>::first_type>;

 (since C++23)
(exposition only*)

template< ranges::input_range Range > using /*range-mapped-t*/ = typename ranges::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<typename ranges::range_value_t<Range>::first_type>, typename ranges::range_value_t<Range>::second_type>;

 (since C++23)
(exposition only*)

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

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

#include <unordered_map>

int main()
{
    // std::unordered_multimap 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_multimap m1 = {std::pair{"foo", 2}, {"bar", 3}}; // guide #2
    std::unordered_multimap 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>