HH\Lib\C\first_keyx

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This is available as C\first_keyx in the www repository.

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

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.'