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FirstKey

hphp/hack/manual/apis/Interfaces/ConstMap/firstKey.md

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:::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 first key in the current ConstMap

Hack
public function firstKey(): ?Tk;

Returns

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