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Hello Marcus, So to be clear, what we are talking about is variable typing and type hints. Variable typing is only done within a class or trait. The dog class has examples of variable typing. I expanded the examples to make a point of what changed: <?php class Dog { private int $dog_weight = 0; private string $dog_breed = "no breed"; private string $dog_color = "no color"; private string $dog_name = "no name"; public function __construct($dog_weight, $dog_breed, $dog_color, $dog_name) { $this->dog_weight = $dog_weight; $this->dog_breed = $dog_breed; $this->dog_color = $dog_color; $this->dog_name = $dog_name; } public function get_properties() : string { return "$this->dog_weight, $this->dog_breed, $this->dog_color, $this->dog_name"; } } $fido = new Dog(42, 'Poodle', 'Brown', 'Fido'); echo $fido->get_properties() . PHP_EOL; $spike = new Dog('Heavy', 'Mutt', 'Orange', 'Spike'); // Generates Fatal error: Uncaught TypeError: Cannot assign string to property Dog::$dog_weight of type int echo $spike->get_properties() . PHP_EOL; The class variable definition lines like this one: "private int $dog_weight = 0" was first introduced in PHP 7.4. Prior to that you could not include the "int" to tell php you wanted $dog_weight to be a int. Furthermore, in my examples, if you try something like passing a string for the assignment, php will generate a runtime error now: "Fatal error: Uncaught TypeError: Cannot assign string to property Dog::$dog_weight of type int" Previously however, PHP did support type hinting for parameters that has a similar function. <?php class Dog { private $dog_weight = 0; private $dog_breed = "no breed"; private $dog_color = "no color"; private $dog_name = "no name"; public function __construct(int $dog_weight, string $dog_breed, string $dog_color, string $dog_name) { $this->dog_weight = $dog_weight; $this->dog_breed = $dog_breed; $this->dog_color = $dog_color; $this->dog_name = $dog_name; } public function get_properties() : string { return "$this->dog_weight, $this->dog_breed, $this->dog_color, $this->dog_name"; } } $fido = new Dog(42, 'Poodle', 'Brown', 'Fido'); echo $fido->get_properties() . PHP_EOL; $spike = new Dog('Heavy', 'Mutt', 'Orange', 'Spike'); // Generates a Fatal error: Uncaught TypeError: Dog::__construct(): Argument #1 ($dog_weight) must be of type int, string given echo $spike->get_properties() . PHP_EOL; This was available in PHP version 7.0. This parameter type hinting has been heavily used, especially when passing objects as parameters, since version 7.0. class Dog { private $dog_weight = 0; private $dog_breed = "no breed"; private $dog_color = "no color"; private $dog_name = "no name"; public function __construct(int $dog_weight, string $dog_breed, string $dog_color, string $dog_name) { $this->dog_weight = $dog_weight; $this->dog_breed = $dog_breed; $this->dog_color = $dog_color; $this->dog_name = $dog_name; } public function get_properties() : string { return "$this->dog_weight, $this->dog_breed, $this->dog_color, $this->dog_name"; } } class Cat { private $cat_breed = 'no breed'; private $cat_name = 'no name'; public function __construct(string $cat_breed, string $cat_name) { $this->cat_breed = $cat_breed; $this->cat_name= $cat_name; } public function get_properties() : string { return "$this->cat_breed, $this->cat_name"; } } class Kennel { private $borders = []; public function addDog(Dog $dog) : void { $this->borders[] = $dog; } public function getBorders() : string { $output = ''; foreach($this->borders as $pet) { $output .= $pet->get_properties() . PHP_EOL; } return $output; } } $kennel = new Kennel(); $fido = new Dog(42, 'Poodle', 'Brown', 'Fido'); $kennel->addDog($fido); $sparky = new Dog(22, 'Mutt', 'Tan', 'Sparky'); $kennel->addDog($sparky); $simba = new Cat('siamese', 'Simba'); echo $simba->get_properties() . PHP_EOL; echo $kennel->getBorders(); $kennel->addDog($simba); //Generates Fatal error: Uncaught TypeError: Kennel::addDog(): Argument #1 ($dog) must be of type Dog, Cat given What has never been possible is add a type to a variable declaration outside of a class definition (as you attempted to do): <?php int $errorCode = 7; //generates a Parse error: syntax error, unexpected '$errorCode' (T_VARIABLE) in 7. //generates Parse error: syntax error, unexpected variable "$errorCode" in 8. One other common type hint is to utilize an interface definition as a parameter type hint: <?php interface HasFeet { public function setFeet(int $number); public function getFeet() : int; } class Duck implements HasFeet { private $nbrFeet; public function setFeet(int $number) { $this->nbrFeet = $number; } public function getFeet() : int { return $this->nbrFeet; } } class Mouse implements HasFeet { private $legs; public function setFeet(int $number) { $this->legs = $number; } public function getFeet() : int { return $this->legs; } } class Fish { private $legs = 0; public function getFeet() : int { return $this->legs; } } class Catalog { private $animals = []; public function addAnimal(HasFeet $animal) { $this->animals[] = $animal; } public function getAnimalFeetCount() : string { $output = ''; foreach($this->animals as $animal) { $output .= 'A ' . get_class($animal) . " has {$animal->getFeet()} feet" . PHP_EOL; } return $output; } } $catalog = new Catalog(); $duck = new Duck(); $duck->setFeet(2); $mouse = new Mouse(); $mouse->setFeet(4); $catalog->addAnimal($duck); $catalog->addAnimal($mouse); echo $catalog->getAnimalFeetCount(); //Generates //A Duck has 2 feet //A Mouse has 4 feet // //Fatal error: Uncaught TypeError: Argument 1 passed to Catalog::addAnimal() must implement interface HasFeet, instance of Fish given PHP 8 has added constructor variable definition through parameter scope & typing: <?php // Prior to 8.0 - Standard class variable initialization class Bike { private $wheels = 0; public function __construct(int $wheels=2) { $this->wheels = $wheels; } public function getWheels() : int { return $this->wheels; } } // PHP 8.0 definition via parameter class Car { public function __construct(private int $wheels=4) { } public function getWheels() : int { return $this->wheels; } } $bike = new Bike(); echo $bike->getWheels() . PHP_EOL; $car = new Car(); echo $car->getWheels() . PHP_EOL; $truck = new Car(18); echo $truck->getWheels() . PHP_EOL; // In PHP 8.01+ // 2 // 4 // 18 So PHP 8 will relieve you of having to define attributes in the class definition, if you define them in the constructor. This works for class parameters as well!