Returns the first "key" in the current Set

public function firstKey(): ?arraykey;

Since Sets do not have keys, it returns the first value.

This method is interchangeable with firstValue().


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


This example shows that firstKey returns the first value in the Set. An empty Set will return null as its first key.

$s = Set {'red', 'green', 'blue', 'yellow'};

$s = Set {};