std::flat_map<Key,T,Compare,KeyContainer,MappedContainer>::insert_or_assign
From cppreference.com
template< class M > std::pair<iterator, bool> insert_or_assign( const key_type& k, M&& obj ); |
(1) | (since C++23) |
template< class M > std::pair<iterator, bool> insert_or_assign( key_type&& k, M&& obj ); |
(2) | (since C++23) |
template< class K, class M > std::pair<iterator, bool> insert_or_assign( K&& k, M&& obj ); |
(3) | (since C++23) |
template< class M > iterator insert_or_assign( const_iterator hint, const key_type& k, M&& obj ); |
(4) | (since C++23) |
template< class M > iterator insert_or_assign( const_iterator hint, key_type&& k, M&& obj ); |
(5) | (since C++23) |
template< class K, class M > iterator insert_or_assign( const_iterator hint, K&& k, M&& obj ); |
(6) | (since C++23) |
1,2) If a key equivalent to
k already exists in the container, assigns std::forward<M>(obj) to the mapped_type corresponding to the key k. If the key does not exist, inserts the new value as if by
- (1,2)
try_emplace(std::forward<decltype(k)>(k), std::forward<M>(obj)), - (4,5)
try_emplace(hint, std::forward<decltype(k)>(k), std::forward<M>(obj)).
The program is ill-formed if either
std::is_assignable_v<mapped_type&, M> or std::is_constructible_v<mapped_type, M> is false.3,6) If a key equivalent to
k already exists in the container, assigns std::forward<M>(obj) to the mapped_type corresponding to the key k. Otherwise, equivalent to
- (3)
try_emplace(std::forward<K>(k), std::forward<M>(obj)), - (6)
try_emplace(hint, std::forward<K>(k), std::forward<M>(obj)).
The conversion from
k into key_type must construct an object u, for which find(k) == find(u) is true. Otherwise, the behavior is undefined. These overloads participate in overload resolution only if :
- The qualified-id
Compare::is_transparentis valid and denotes a type. std::is_constructible_v<key_type, K>istrue.std::is_assignable_v<mapped_type&, M>istrue.std::is_constructible_v<mapped_type, M>istrue.
| Information on iterator invalidation is copied from here |
Parameters
| k | - | the key used both to look up and to insert if not found |
| hint | - | iterator to the position before which the new element will be inserted |
| obj | - | the value to insert or assign |
Return value
1-3) The
bool component is true if the insertion took place and false if the assignment took place. The iterator component is pointing at the element that was inserted or updated.4-6) Iterator pointing at the element that was inserted or updated.
Complexity
1-3) Same as for
emplace.4-6) Same as for
emplace_hint.Notes
insert_or_assign returns more information than operator[] and does not require default-constructibility of the mapped type.
Example
Run this code
#include <flat_map>
#include <iostream>
#include <string>
void print_node(const auto& node)
{
std::cout << '[' << node.first << "] = " << node.second << '\n';
}
void print_result(auto const& pair)
{
std::cout << (pair.second ? "inserted: " : "assigned: ");
print_node(*pair.first);
}
int main()
{
std::flat_map<std::string, std::string> map;
print_result(map.insert_or_assign("a", "apple"));
print_result(map.insert_or_assign("b", "banana"));
print_result(map.insert_or_assign("c", "cherry"));
print_result(map.insert_or_assign("c", "clementine"));
for (const auto& node : map)
print_node(node);
}
Output:
inserted: [a] = apple
inserted: [b] = banana
inserted: [c] = cherry
assigned: [c] = clementine
[a] = apple
[b] = banana
[c] = clementine
See also
| access or insert specified element (public member function) | |
| access specified element with bounds checking (public member function) | |
| inserts elements (public member function) | |
| constructs element in-place (public member function) | |
| inserts in-place if the key does not exist, does nothing if the key exists (public member function) |