intersect

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 only the elements of the first Traversable that appear in all the other ones

namespace HH\Lib\Vec;

function intersect<Tv as arraykey>(
  Traversable<Tv> $first,
  Traversable<Tv> $second,
  Container<Tv> ...$rest,
): vec<Tv>;

Duplicate values are preserved.

Time complexity: O(n + m), where n is size of $first and m is the combined size of $second plus all the ...$rest Space complexity: O(n), where n is size of $first

Parameters

• Traversable<Tv>$first
• Traversable<Tv>$second
• Container<Tv>...$rest

Returns

• vec<Tv>

Examples

$example_vec1 = vec[1,2,3,4,5];
$example_vec2 = vec[1,3];

$result = Vec\intersect($example_vec1, $example_vec2);
print_r($result);
//result: [1,3]

$example_vec3 = vec[6,7];
$result = Vec\intersect($example_vec1, $example_vec3);
print_r($result);
//result: []