Lastx

:::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 last element of the given Traversable, or throws if the Traversable is empty

namespace HH\Lib\C;

function lastx<T>(
  Traversable<T> $traversable,
): T;

• For possibly empty Traversables, see C\last.
• For single-element Traversables, see C\onlyx.

Time complexity: O(1) if $traversable is a Container, O(n) otherwise. Space complexity: O(1)

Parameters

• Traversable<T>$traversable

Returns

• T

Examples

$strings = vec["a", "b", "c"];
$last_string = C\lastx($strings);
echo "Last string in traversable: $last_string \n";
//Output: Last string in traversable: c 

$empty_traversable = vec[];
$last_element = C\lastx($empty_traversable);
//Output: Hit a php exception : exception 'InvariantViolationException' with message
//'HH\Lib\C\lastx: Expected at least one element.'