user.php

<?php

class User {

    protected $firstName;
    protected $lastName;
    protected $email;

    public function setFirstName(string $firstName): self
    {
        $this->firstName = $firstName;

        return $this;
    }

    public function getFirstName(): string
    {
        return $this->firstName;
    }

    public function setLastName(string $lastName): self
    {
        $this->lastName = $lastName;

        return $this;
    }

    public function getLastName(): string
    {
        return $this->lastName;
    }

    public function setEmail(string $email): self
    {
        $this->email = $email;

        return $this;
    }

    public function getEmail(): string
    {
        return $this->email;
    }

    public function __toString(): string
    {
        return $this->getFirstName() . $this->getLastName();
    }
}

$user = new User();
$user->setFirstName('John');
// ->setLastName('Doe')
// ->setEmail('john.doe@example.com');

echo $user->getFirstName();