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unique

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 a new vec containing each element of the given Traversable exactly once

namespace HH\Lib\Vec;

function unique<Tv as arraykey>(
  Traversable<Tv> $traversable,
): vec<Tv>;

The Traversable must contain arraykey values, and strict equality will be used.

For non-arraykey elements, see Vec\unique_by().

Time complexity: O(n) Space complexity: O(n)

Parameters​

Returns​

  • vec<Tv>

Examples​

$vector = vec[1, 1, 2, 3, 4, 4, 4, 4];
$uniqueVals = Vec\unique($vector);
\print_r($uniqueVals);