LastKey

:::info[Note] This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information. :::

Returns the last "key" in the current MutableSet

public function lastKey(): ?arraykey;

Since sets do not have keys, it returns the last value.

This method is interchangeable with lastValue().

Returns

• ?arraykey - The last value in the current MutableSet, or null if the current MutableSet is empty.