std::flat_map<Key,T,Compare,KeyContainer,MappedContainer>:: insert_or_assign

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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
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
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 :
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)
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