std::flat_map::insert_or_assign(3)

NAME
std::flat_map::insert_or_assign - std::flat_map::insert_or_assign

Synopsis
   template< class M >
   std::pair<iterator, bool> insert_or_assign( const key_type& k, M&& (1) (since C++23)
   obj );
   template< class M >
   std::pair<iterator, bool> insert_or_assign( key_type&& k, M&& obj (2) (since C++23)
   );
   template< class K, class M > (3) (since C++23)
   std::pair<iterator, bool> insert_or_assign( K&& k, M&& obj );
   template< class M >
   iterator insert_or_assign( const_iterator hint, const key_type& k, (4) (since C++23)
   M&& obj );
   template< class M >
   iterator insert_or_assign( const_iterator hint, key_type&& k, M&& (5) (since C++23)
   obj );
   template< class K, class M > (6) (since C++23)
   iterator insert_or_assign( const_iterator hint, K&& k, M&& obj );
   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_transparent is valid and denotes a type.
     * std::is_constructible_v<key_type, K> is true.
     * std::is_assignable_v<mapped_type&, M> is true.
     * std::is_constructible_v<mapped_type, M> is true.
    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
   operator[] access or insert specified element
               (public member function)
   at access specified element with bounds checking
               (public member function)
   insert inserts elements
               (public member function)
   emplace constructs element in-place
               (public member function)
               inserts in-place if the key does not exist, does nothing if the key
   try_emplace exists
               (public member function)