Access or insert the specified element.
value& operator( string_view key);
Returns a reference to the value that is mapped to a key equivalent to key, performing an insertion of a null value if such key does not already exist.
If an insertion occurs and results in a rehashing of the container, all
iterators are invalidated. Otherwise iterators are not affected. References
are not invalidated. Rehashing occurs only if the new number of elements
is greater than
Constant on average, worst case linear in
Strong guarantee. Calls to
A reference to the mapped value.
The key of the element to find.