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contains_key

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 true if the given KeyedContainer contains the key

namespace HH\Lib\C;

function contains_key<Tk1 as arraykey, Tk2 as arraykey, Tv>(
  KeyedContainer<Tk1, Tv> $container,
  Tk2 $key,
): bool;

Time complexity: O(1) Space complexity: O(1)

Parameters​

Returns​

  • bool

Examples​

$dict = dict["key_1" => "a", "key_2" => "b"];
$contains_key_result_1 = C\contains_key($dict, "key_1");
echo "First contains key result: $contains_key_result_1\n";
//Output: First contains key result: true

$contains_key_result_2 = C\contains_key($dict, "key_3");
echo "Second contains key result: $contains_key_result_2\n";
//Output: Second contains key result: false

$contains_key_result_3 = C\contains_key($dict, "");
echo "Third contains key result: $contains_key_result_3\n";
//Output: Third contains key result: false