Value object external validation

Country.php

<?php

final class Country
{
    private string $countryCode;
    
    private function __construct(string $countryCode)
    {
        $this->countryCode = $countryCode;
    }
    
    /**
     * @param callable(string): bool $f
     */
    public static function existing(callable $exists, string $countryCode): self
    {
        if (!$exists($countryCode)) {
            throw new \Exception('no no no!!!')
        }
        
        return new self($countryCode);
    }
}