At

:::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 value of the field $index of $shape, throws if the field is missing

public static function at(
  shape() $shape,
  arraykey $index,
);

Use this to access optional fields on shapes.

Parameters

• shape() $shape
• arraykey $index