|null $function Optional scoring function: * ['saturation' => ['pivot' => 8]] | ['log' => ['scaling_factor' => 4]] * | ['sigmoid' => ['pivot' => 7, 'exponent' => 0.6]] | ['linear' => new \stdClass()]. */ public function __construct( private string $field, private array|null $function = null, private float $boost = 1.0, ) { } public function key(): string { return 'rank_feature_' . $this->field; } /** * @return array> */ public function toArray(): array { $body = [ 'field' => $this->field, 'boost' => $this->boost, ]; if ($this->function !== null) { foreach ($this->function as $name => $config) { $body[$name] = $config; } } return [ 'rank_feature' => $body, ]; } }