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 at the specified key in the current Pair

public function at(
  int $key,
): mixed;

If the key is not present, an exception is thrown. This essentially means if you specify a key other than 0 or 1, you will get an exception. If you don't want an exception to be thrown, use get() instead.

$v = $p->at($k)" is semantically equivalent to $v = $p[$k].

Parameters

• int $key - the key from which to retrieve the value.

Returns

• mixed - The value at the specified key; or an exception if the key does not exist.

Examples

This example prints the first and second values of the Pair:

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

// Print the first element
\var_dump($p->at(0));

// Print the second element
\var_dump($p->at(1));

This example throws an OutOfBoundsException because a Pair only has the indexes 0 and 1:

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

// Index 2 doesn't exist because pairs always have exactly two elements
\var_dump($p->at(2));