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firstKey

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 first key in the current Vector

public function firstKey(): ?int;

Returns​

  • ?int - The first key (an integer) in the current Vector, or null if the Vector is empty.

Examples​

The following example gets the first key from Vector. An empty Vector will return null as its first key.

$v = Vector {'red', 'green', 'blue', 'yellow'};
\var_dump($v->firstKey());

$v = Vector {};
\var_dump($v->firstKey());