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findx

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 the first value of the given Traversable for which the predicate returns true, or throws if no such value is found

namespace HH\Lib\C;

function findx<T>(
  Traversable<T> $traversable,
  (function(T): bool) $value_predicate,
): T;

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

Parameters​

Returns​

  • T

Examples​

$strings = vec["a", "b", "c", "d"];
$predicate_result_1 = C\findx($strings, $x ==> $x == "a");
echo "First predicate: $predicate_result_1\n";
//Output: First predicate: a

$predicate_result_2 = C\findx($strings, $x ==> $x == "z");
//Output: Hit a php exception : exception 'InvariantViolationException' 
//with message 'HH\Lib\C\findx: Couldn't find target value.'