References

Scalar Types

Passing by value (Assignment)

$name1 = "test";
var_dump($name1); //=> string(4) "test"

// Passing by value
$name2 = $name1;
$name2 = "new test";
var_dump($name1); //=> string(4) "test"
var_dump($name2); //=> string(10) "new test"

Passing by value (Function)

$num = 10;
function plusOne($a) {
  return ++$a;
}
var_dump($num);          //=> int(10)
var_dump(plusOne($num)); //=> int(11)
var_dump($num);          //=> int(10)

Passing by reference (Assignment)

$name1 = "test";
var_dump($name1); //=> string(4) "test"

// Passing by reference
$name2 = &$name1;
$name2 = "final test";
var_dump($name1); //=> string(10) "final test"
var_dump($name2); //=> string(10) "final test"

$name1 = "test";
var_dump($name1); //=> string(4) "test"

// Passing by reference
$name2 = &$name1;
$name2 = null;
var_dump($name1); //=> NULL
var_dump($name2); //=> NULL

Passing by reference (Function)

$num = 10;
function plusOne(&$a) {
  return ++$a;
}
var_dump($num);          //=> int(10)
var_dump(plusOne($num)); //=> int(11)
var_dump($num);          //=> int(11)

Compound Types (Array)

Passing by value (Assignment)

$person = ['name' => 'fulano', 'email' => 'fulano@email'];

// Passing by value
$person2 = $person;
$person2['name'] = 'sicrano';
echo $person['name']; //=> fulano

Passing by reference (Assignment)

$person = ['name' => 'fulano', 'email' => 'fulano@email'];

// Passing by reference
$person2 = &$person;
$person2['name'] = 'sicrano';
echo $person['name']; //=> sicrano

$person = ['name' => 'fulano', 'email' => 'fulano@email'];

// Passing by reference
$person2 = &$person;
$person2 = null;
var_dump($person);  //=> NULL
var_dump($person2); //=> NULL

Compound Types (Object)

Passing by value with clone (Assignment)

class Car {
  public $numberOfDoors;
  public $howFast;
}

$myCar = new Car();
$myCar->numberOfDoors = 4;
$myCar->howFast = 150;
$myCar->power = 200;
print_r($myCar);
//=>
// Car Object
// (
//   [numberOfDoors] => 4
//   [howFast] => 150
//   [power] => 200
// )

$myCar2 = clone $myCar;
$myCar2->howFast = 400;
print_r($myCar);
//=>
// Car Object
// (
//   [numberOfDoors] => 4
//   [howFast] => 150
//   [power] => 200
// )

clone object

Passing by reference of identifier (Assignment)

$myCar = new stdClass;
$myCar->numberOfDoors = 4;
$myCar->howFast = 150;
print_r($myCar);
//=>
// stdClass Object
// (
//  [numberOfDoors] => 4
//  [howFast] => 150
// )

$myCar2 = $myCar;
$myCar2->power = 110;
print_r($myCar);
//=>
// stdClass Object
// (
//  [numberOfDoors] => 4
//  [howFast] => 150
//  [power] => 110
// )

ref object

$myCar = new stdClass;
$myCar->numberOfDoors = 4;
$myCar->howFast = 150;

$myCar2 = $myCar;
$myCar2->power = 110;

$myCar = null;
print_r($myCar2);
//=>
// stdClass Object
// (
//  [numberOfDoors] => 4
//  [howFast] => 150
//  [power] => 110
// )

Passing by reference of value (Assignment)

$myCar = new stdClass;
$myCar->numberOfDoors = 4;
$myCar->howFast = 150;
print_r($myCar);
//=>
// stdClass Object
// (
//  [numberOfDoors] => 4
//  [howFast] => 150
// )

$myCar2 = &$myCar;
$myCar2->power = 110;
print_r($myCar);
//=>
// stdClass Object
// (
//  [numberOfDoors] => 4
//  [howFast] => 150
//  [power] => 110
// )

ref object

$myCar = new stdClass;
$myCar->numberOfDoors = 4;
$myCar->howFast = 150;

$myCar2 = &$myCar;
$myCar2->power = 110;

$myCar = null;
var_dump($myCar2); //=> NULL

Passing by value (Statement - foreach)

$names = [0 => fulano, 'admin' => sicrano, 'client' => beltrano];

foreach($names as $key=>$name){
  $name .= 'sufix';
}
print_r($names);
//=>
// Array
// (
//   [0] => fulano
//   [admin] => sicrano
//   [client] => beltrano
// )

Passing by reference (Statement - foreach)

$names = [0 => fulano, 'admin' => sicrano, 'client' => beltrano];

foreach($names as $key=>&$name){
  $name .= 'sufix';
}
print_r($names);
//=>
// Array
// (
//   [0] => fulanosufix
//   [admin] => sicranosufix
//   [client] => beltranosufix
// )

References