deduction guides for std::unordered_multimap
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,
typename /*see below*/::size_type = /*see below*/,
Hash = Hash(), Pred = Pred(), Alloc = Alloc())
-> unordered_multimap<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_multimap(std::initializer_list<std::pair<Key, T>>,
typename /*see below*/::size_type = /*see below*/,
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>,
std::hash<iter_key_t<InputIt>>,
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>,
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_multimap(InputIt, InputIt, typename /*see below*/::size_type, Hash, Alloc)
-> unordered_multimap<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_multimap(std::initializer_list<std::pair<Key, T>>,
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>>,
typename /*see below*/::size_type, Hash, Alloc)
-> unordered_multimap<Key, T, Hash, std::equal_to<Key>, Alloc>; |
(8) | (since C++17) |
where the type aliases iter_key_t, iter_val_t, iter_to_alloc_t are defined as if as follows.
template< class InputIt >
using iter_key_t = std::remove_const_t<
typename std::iterator_traits<InputIt>::value_type::first_type>; |
(exposition only) | |
template< class InputIt > using iter_val_t = typename std::iterator_traits<InputIt>::value_type::second_type; |
(exposition only) | |
template< class InputIt > using iter_to_alloc_t = std::pair< std::add_const_t<typename std::iterator_traits<InputIt>::value_type::first_type>, typename std::iterator_traits<InputIt>::value_type::second_type > |
(exposition only) |
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.
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 take std::pair<const Key, T> |
use std::pair<Key, T> |
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