A lookup mapper is a class that implements Kiboko\Contract\Mapping\CompiledMapperInterface.
Its purpose is to merge the result of the lookup back into your line.
$output is your line, and $input is the result of the lookup.
<?php
declare(strict_types=1);
namespace Acme\Custom;
use Kiboko\Contract\Mapping\CompiledMapperInterface;
class LookupMapper implements CompiledMapperInterface
{
public function __invoke($input, $output = null)
{
$output['actual_customer_id'] = $input['id'];
return $output;
}
}