Serializable Value Object

Customer.php

<?php
final class Customer implements \JsonSerializable
{
    private CustomerId $id;

    private FullName $name;

    public function __construct(CustomerId $id, FullName $name)
    {
        $this->id = $id;
        $this->name = $name;
    }

    public function id(): CustomerId
    {
        return $this->id;
    }

    public function name(): FullName
    {
        return $this->name;
    }

    public function jsonSerialize(): array
    {
        return get_object_vars($this);
    }
}

CustomerId.php

<?php
final class CustomerId implements \JsonSerializable
{
    private string $value;

    /**
     * @var self[]
     */
    private static array $instances = [];

    private function __construct(string $value)
    {
        $this->value = $value;
    }

    private static function constant(string $value): self
    {
        return self::$instances[$value] ?? self::$instances[$value] = new self($value);
    }

    public static function fromString(string $value): self
    {
        return self::constant($value);
    }

    public function toString(): string
    {
        return $this->value;
    }

    public function __toString(): string
    {
        return $this->toString();
    }

    public function jsonSerialize(): string
    {
        return $this->value;
    }

    public function __clone()
    {
        throw new \RuntimeException('Cloning not supported');
    }

    public function __sleep()
    {
        throw new \RuntimeException('Serialization not supported');
    }

    public function __wakeup()
    {
        throw new \RuntimeException('Deserialization not supported');
    }
}