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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 Map

public function firstKey(): ?Tk;

Returns​

  • ?Tk - The first key in the current Map, or null if the Map is empty.

Examples​

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

$m = Map {
  'red' => '#ff0000',
  'green' => '#00ff00',
  'blue' => '#0000ff',
  'yellow' => '#ffff00',
};
\var_dump($m->firstKey());

$m = Map {};
\var_dump($m->firstKey());