HH\Lib\C\first_keyx
Returns the first key of the given KeyedTraversable, or throws if the KeyedTraversable is empty
namespace HH\Lib\C;
function first_keyx<Tk, Tv>(
KeyedTraversable<Tk, Tv> $traversable,
): Tk;
For possibly empty Traversables, see C\first_key.
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"];
$first_keyx_result_1 = C\first_keyx($dict);
echo "First first keyx result: $first_keyx_result_1\n";
//Output: First first keyx result: key_1
$empty_dict = dict[];
$first_keyx_result_2 = C\first_keyx($empty_dict);
//Output: Hit a php exception : exception 'InvariantViolationException' with message
//'HH\Lib\C\first_keyx: Expected at least one element.'