The document summarizes new features coming in PHP 7.4, including typed properties, arrow functions, the nullsafe operator, and array spread syntax. It also discusses future language features like property accessors and generics. Some deprecations are noted, such as changes to ternary operator and concatenation precedence to avoid ambiguity.

1. Typed Properties and more:
What’s coming in PHP 7.4?
Nikita Popov

3. Release schedule (tentative)
Now
June 6th PHP 7.4 Alpha 1
July 18th PHP 7.4 Beta 1 – Feature freeze
November 21st PHP 7.4 GA Release

4. Release schedule (tentative)
Now
June 6th PHP 7.4 Alpha 1
July 18th PHP 7.4 Beta 1 – Feature freeze
November 21st PHP 7.4 GA Release
December 2020 PHP 8.0 Release
≈

5. Overview
●
FFI & Preloading
●
Typed Properties
●
Arrow Functions
●
Covariant Return Types
●
??=
●
Array Spread Operator
●
WeakReference
●
Deprecations

6. Overview
●
FFI & Preloading => See Dmitry Stogov’s talk!
●
Typed Properties
●
Arrow Functions
●
Covariant Return Types
●
??=
●
Array Spread Operator
●
WeakReference
●
Deprecations

7. Typed Properties
class User {
public int $id;
public string $name;
}
$user = new User;
$user->id = 42;
$user->name = [];
// Uncaught TypeError: Typed property User::$name
// must be string, array used

8. Nullability & Initialization
class User {
public int $id; // no null default
public ?string $name; // also no null default (!)
}

9. Nullability & Initialization
class User {
public int $id; // no null default
public ?string $name; // also no null default (!)
}
$user = new User;
var_dump($user->name);
// Uncaught Error: Typed property User::$name must
// not be accessed before initialization

10. Nullability & Initialization
class User {
public int $id;
public ?string $name = null;
}
$user = new User;
var_dump($user->name); // NULL

11. References
class User {
public int $id = 42;
public string $name = "nikic";
}
$user = new User;
$id =& $user->id;
$id = "not an id";
// Uncaught TypeError: Cannot assign string to
// reference held by property User::$id of type int

12. Poor Man’s Intersection Types
class Test {
public ?Traversable $traversable;
public ?Countable $countable;
public $both = null;
}
$test = new Test;
$test->traversable =& $test->both;
$test->countable =& $test->both;
$test->both = new ArrayIterator;

13. Poor Man’s Intersection Types
class Test {
public ?Traversable $traversable;
public ?Countable $countable;
public $both = null;
}
$test = new Test;
$test->traversable =& $test->both;
$test->countable =& $test->both;
$test->both = new ArrayIterator;
Effectively ?(Traversable&Countable)

14. Poor Man’s Intersection Types
class Test {
public ?Traversable $traversable;
public ?Countable $countable;
public $both = null;
}
$test = new Test;
$test->traversable =& $test->both;
$test->countable =& $test->both;
$test->both = new AppendIterator;
// Uncaught TypeError: Cannot assign AppendIterator
// to reference held by property Test::$countable
// of type ?Countable

15. Poor Man’s Typed Variables
int $i = 0;
$i = "foobar";

16. Poor Man’s Typed Variables
$i =& int(0);
$i = "foobar";
// Uncaught TypeError: Cannot assign string to
// reference held by property class@anonymous::$prop
// of type int

17. Poor Man’s Typed Variables
function &int(int $i) {
$obj = new class { public int $prop; };
$obj->prop = $i;
$GLOBALS['huge_memory_leak'][] = $obj;
return $obj->prop;
}
$i =& int(0);
$i = "foobar";
// Uncaught TypeError: Cannot assign string to
// reference held by property class@anonymous::$prop
// of type int

18. Public Typed Properties?
class User {
private $name;
public function getName(): string {
return $this->name;
}
public function setName(string $name): void {
$this->name = $name;
}
}

19. Public Typed Properties?
class User {
public string $name;
}

20. Public Typed Properties?
class User {
public string $name;
}
What if additional validation will be needed?

21. Future: Property Accessors?
class User {
public string $name {
get;
set($name) {
if (strlen($name) == 0)
throw new Exception(
'Name cannot be empty');
$this->name = $name;
}
};
}

22. Arrow Functions
array_filter(
$values,
function($v) use($allowedValues) {
return in_array($v, $allowedValues);
}
);

23. Arrow Functions
array_filter(
$values,
fn($v) => in_array($v, $allowedValues)
);

24. Arrow Functions
array_filter(
$values,
fn($v) => in_array($v, $allowedValues)
);
Implicit use($allowedValues)

25. By-Value Binding
$i = 0;
$fn = fn() => $i++;
$fn();
var_dump($i); // int(0)

26. By-Value Binding
$fns = [];
foreach ([1, 2, 3] as $i) {
$fns[] = fn() => $i;
}
foreach ($fns as $fn) {
echo $fn() . " ";
}
// Prints: 1 2 3
// Not: 3 3 3 (would happen with by-reference)

27. Syntax – Why fn?
array_filter(
$values,
$v => in_array($v, $allowedValues)
);
ECMAScript syntax

28. Syntax – Array Ambiguity
$array = [
$a => $a + $b,
$x => $x * $y,
];
Array of arrow functions?
Or just a key-value map?

29. Syntax – Parsing
// Looks like: Assignment expression
($x = [42] + ["foobar"]) => $x;
// Looks like: Constant lookup + bitwise and
(Type &$x) => $x;
// Looks like: Ternary operator
$a ? ($b): Type => $c : $d;

30. Syntax – Parsing
// Looks like: Assignment expression
($x = [42] + ["foobar"]) => $x;
// Looks like: Constant lookup + bitwise and
(Type &$x) => $x;
// Looks like: Ternary operator
$a ? ($b): Type => $c : $d;
Need special handling starting at (
But only know it’s an arrow function at =>

31. Future: Block Syntax
array_filter(
$values,
fn($v) => in_array($v, $allowedValues)
);

32. Future: Block Syntax
array_filter(
$values,
fn($v) {
// More code...
return in_array($v, $allowedValues);
}
);

33. Future: Block Syntax
array_filter(
$values,
fn($v) {
// More code...
return in_array($v, $allowedValues);
}
);
Basically like normal closure syntax,
but with implicit variable capture

34. Covariant Return Types
class A {}
class B extends A {}
class Producer {
public function produce(): A {}
}
class ChildProducer extends Producer {
public function produce(): B {}
}
Sound because $childFactory->create() still instanceof A.

35. Common Case: Self
class Foo {
public function fluent(): self {}
}
class Bar extends Foo {
public function fluent(): self {}
}

36. Ordering Issues
class A {
public function method(): B {}
}
class B extends A {
public function method(): C {}
}
class C extends B {}

37. Ordering Issues
class A {
public function method(): B {}
}
class B extends A {
public function method(): C {}
}
class C extends B {}
Sound, but class C not available when verifying B.
=> No way to reorder classes “correctly”.
=> Will only work with autoloading (for now).

38. Contravariant Parameter Types
class A {}
class B extends A {}
class Consumer {
public function comsume(B $value) {}
}
class ChildConsumer extends Consumer {
public function comsume(A $value) {}
}
Sound, but rarely useful.

39. Covariant Parameter Types?
interface Event { ... }
class SpecificEvent implements Event { ... }
interface EventHandler {
public function handle(Event $e);
}
class SpecificEventHandler implements EventHandler {
public function handle(SpecificEvent $e) {}
}
Unsound, will never work!

40. Future: Generics
interface Event { ... }
class SpecificEvent implements Event { ... }
interface EventHandler<E: Event> {
public function handle(E $e);
}
class SpecificEventHandler
implements EventHandler<SpecificEvent>
{
public function handle(SpecificEvent $e) {}
}

41. ??=
$options["something"] ??= new DefaultObject;
// Roughly equivalent to:
$options["something"] =
$options["something"] ?? new DefaultObject;

42. ??=
$options["something"] ??= new DefaultObject;
Only created if $options["something"] is null

43. Array spread operator
$array = [3, 4, 5];
return call(1, 2, ...$array); // call(1, 2, 3, 4, 5)
$array = [3, 4, 5];
return [1, 2, ...$array]; // [1, 2, 3, 4, 5]

44. Array spread operator
$array = new ArrayIterator([1, 2, 3]);
return call(1, 2, ...$array); // call(1, 2, 3, 4, 5)
$array = new ArrayIterator([1, 2, 3]);
return [1, 2, ...$array]; // [1, 2, 3, 4, 5]

45. Array spread operator
$array = ['y' => 'b', 'z' => 'c'];
return ['x' => 'a', ...$array];
// Uncaught Error: Cannot unpack array with
// string keys

46. Future: … in destructuring
[$head, ...$tail] = $array;

47. Future: … in destructuring
$array = [2 => 2, 1 => 1, 0 => 0];
[$head, ...$tail] = $array;
What happens?

48. WeakReference
$object = new stdClass;
$weakRef = WeakReference::create($object);
var_dump($weakRef->get()); // object(stdClass)#1
unset($object);
var_dump($weakRef->get()); // NULL

49. WeakReference
$this->data[get_object_id($object)]
= [WeakReference::create($object), $data];

50. WeakReference
$this->data[get_object_id($object)]
= [WeakReference::create($object), $data];
Will be reused once
object is destroyed

51. WeakReference
$this->data[get_object_id($object)]
= [WeakReference::create($object), $data];
Will be reused once
object is destroyed
Check $weakRef->get() != null
to know whether the entry is still valid

52. WeakReference
$this->data[get_object_id($object)]
= [WeakReference::create($object), $data];
Will be reused once
object is destroyed
Check $weakRef->get() != null
to know whether the entry is still valid
Problem: Doesn’t keep $object alive, but keeps dead cache entry

53. Future: WeakMap
$this->data = new WeakMap();
$this->data[$object] = $data;
Does not keep $object alive; immediately
drops cache entry when object destroyed

54. Deprecations
Surprisingly few for now…
…there will probably be more.

55. Ternary Associativity
return $a == 1 ? 'one'
: $a == 2 ? 'two'
: 'other';
// was intended as:
return $a == 1 ? 'one'
: ($a == 2 ? 'two'
: 'other');
// but PHP interprets it as:
return ($a == 1 ? 'one'
: $a == 2) ? 'two'
: 'other';

56. Ternary Associativity
return $a == 1 ? 'one' // Deprecated in 7.4.
: $a == 2 ? 'two' // Compile error in 8.0.
: 'other';
// was intended as:
return $a == 1 ? 'one'
: ($a == 2 ? 'two'
: 'other');
// but PHP interprets it as:
return ($a == 1 ? 'one'
: $a == 2) ? 'two'
: 'other';

57. Concatenation Precedence
$a = 1;
$b = 2;
echo "Sum: " . $a+$b;
// was intended as:
echo "Sum: " . ($a+$b);
// but PHP interprets it as:
echo ("Sum: " . $a)+$b;

58. Concatenation Precedence
$a = 1;
$b = 2;
echo "Sum: " . $a+$b; // Deprecated in PHP 7.4
// was intended as:
echo "Sum: " . ($a+$b); // New behavior in PHP 8.0
// but PHP interprets it as:
echo ("Sum: " . $a)+$b;

59. Short Open Tags (?)
●
<? deprecated in 7.4, removed in 8.0
●
Only <?php and <?= supported
●
(???) short_open_tag default value from On to
Off in 7.4
Disclaimer: RFC accepted, but much push-back after voting.

60. 3v4l.org

61. Travis CI
php:
- 7.3
- 7.4snapshot
- nightly
install:
- composer install --ignore-platform-reqs
PHPUnit claims it is not
PHP 8 compatible (it is)PHP 8

62. Docker
●
https://github.com/devilbox/docker-php-fpm-7.4
●
https://github.com/devilbox/docker-php-fpm-8.0

63. Thank You!
Questions?