Unique

:::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 a new dict in which each value appears exactly once

namespace HH\Lib\Dict;

function unique<Tk as arraykey, Tv as arraykey>(
  KeyedTraversable<Tk, Tv> $traversable,
): dict<Tk, Tv>;

In case of duplicate values, later keys will overwrite the previous ones.

For non-arraykey values, see Dict\unique_by().

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

Parameters

• KeyedTraversable<Tk,Tv> $traversable

Returns

• dict<Tk, Tv>