Slides for PHPRussia 2019 talk on new features in PHP 7.4.

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?