<?php
class User
{
    public $firstName;
    public $lastName;
    public $email;

function __construct(){
    echo "Constructor in action";
}

function setFirstName($fname){
    $this->firstName = $fname;
}

function setLastName($lname){
    $this->lastName = $fname;
}

function setEmail($email){
    $this->email = $fname;
}

function __toString(){
    return $this->firstName." ".$this->lastName." ".$this->email;
}

function __destruct(){
    echo "Class destroyed";
}

}

$user = new User();

$user->setFirstName("John")->setLastName(" Doe")->setEmail(" email@email.com");

echo $user;
?>

PHP Fatal error: Uncaught Error: Call to a member function setLastName() on null in index.php:36 Stack trace: #0 {main} thrown in index.php on line 36

$user = new User();
$user->setFirstName("John");
$user->setLastName("Doe");
$user->setEmail("John@doe.com");