cpp/container/unordered set/emplace hint

Inserts a new element to the container, using as a suggestion where the element should go. The element is constructed in-place, i.e. no copy or move operations are performed.

The constructor of the element is called with exactly the same arguments as supplied to the function, forwarded with.

Return value
Returns an iterator to the newly inserted element.

If the insertion failed because the element already exists, returns an iterator to the already existing element with the equivalent key.

Exceptions
If an exception is thrown by any operation, this function has no effect (strong exception guarantee).

Complexity
Amortized constant on average, worst case linear in the size of the container.