ContainsKey

:::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. :::

Checks whether a provided key exists in the current Pair

public function containsKey<Tu super int>(
  Tu $key,
): bool;

This will only return true for provided keys of 0 and 1 since those are the only two keys that can exist in a Pair.

Parameters

• Tu $key

Returns

• bool - true if the provided key exists in the Pair; false otherwise. This will only return true if the provided key is 0 or 1.

Examples

$p = Pair {'foo', -1.5};

// Prints "true", since index 0 is the first value
\var_dump($p->containsKey(0));

// Prints "true", since index 1 is the second value
\var_dump($p->containsKey(1));

// Prints "false", since a Pair only has index 0 and index 1
\var_dump($p->containsKey(2));