HH\Lib\C\first_key
Returns the first key of the given KeyedTraversable, or null if the KeyedTraversable is empty
namespace HH\Lib\C;
function first_key<Tk, Tv>(
KeyedTraversable<Tk, Tv> $traversable,
): ?Tk;
For non-empty Traversables, see C\first_keyx.
Time complexity: O(1) Space complexity: O(1)
Parameters
KeyedTraversable<Tk,Tv> $traversable
Returns
?Tk
Examples
$dict = dict["key_1" => "a", "key_2" => "b", "key_3" => "c"];
$first_key_result_1 = C\first_key($dict);
echo "First first key result: $first_key_result_1\n";
//Output: First first key result: key_1
$empty_dict = dict[];
$first_key_result_2 = C\first_key($empty_dict);
$first_key_result_2_as_string = $first_key_result_2 ?? "null";
echo "Second first key result: $first_key_result_2_as_string\n";
//Output: Second first key result: null