HH\Lib\C\find_key
Returns the key of the first value of the given KeyedTraversable for which the predicate returns true, or null if no such value is found
namespace HH\Lib\C;
function find_key<Tk, Tv>(
KeyedTraversable<Tk, Tv> $traversable,
(function(Tv): bool) $value_predicate,
): ?Tk;
Time complexity: O(n) Space complexity: O(1)
Parameters
KeyedTraversable<Tk,Tv> $traversable(function(Tv): bool) $value_predicate
Returns
?Tk
Examples
$dict = dict["key_1" => "a", "key_2" => "b", "key_3" => "c"];
$predicate_result_1 = C\find_key($dict, $x ==> $x == "a");
echo "First predicate: $predicate_result_1\n";
//Output: First predicate: key_1
$predicate_result_2 = C\find_key($dict, $x ==> $x == "z");
$predicate_result_2_as_string = $predicate_result_2 ?? "null";
echo "Second predicate: $predicate_result_2_as_string\n";
//Output: Second predicate: null
$repeat_dict = dict["key_1" => "a", "key_2" => "b", "key_3" => "c", "key_4" => "a"];
$predicate_result_3 = C\find_key($dict, $x ==> $x == "a");
echo "Repeat_predicate: $predicate_result_3\n";
//Output: Repeat_predicate: key_1