Concat - Hhvm — ContextQMD

:::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 Vector that is the concatenation of the values of the current Set and the values of the provided Traversable

Hack

public function concat<Tu super Tv>(
  Traversable<Tu> $traversable,
): Vector<Tu>;

The values of the provided Traversable is concatenated to the end of the current Set to produce the returned Vector.

Guide

Constraints

Parameters

Traversable<Tu>$traversable - The Traversable to concatenate to the current Set.

Returns

Vector<Tu> - The concatenated Vector.

Examples

This example creates new Sets by concatenating other Traversables. Unlike Set::addAll() this method returns a new Set (not a shallow copy).

basic-usage.hack

$s = Set {'red'};

// Add all the values in a Vector
$s1 = $s->concat(Vector {'green', 'blue'});

// Add all the values in an array
$s2 = $s1->concat(varray['yellow', 'purple']);

\var_dump($s); // $s contains 'red'
\var_dump($s1); // $s1 contains 'red', 'green', 'blue'
\var_dump($s2); // $s2 contains 'red', 'green', 'blue', 'yellow', 'purple'