What’s new in PHP 8 – Part 1(New features)

PHP 8 is here! It was released on November 26, 2020. You can download it here. It’s a new major version, which means that it will introduce some breaking changes, as well as lots of new features and performance improvements.

Besides breaking changes, PHP 8 also brings a nice set of new features such as the JIT compiler, union types, attributes, and more. Let’s start with what’s new in php 8, it’s quite a list!

New features Explained:

Union types rfc

Given the dynamically typed nature of PHP, there are lots of cases where union types can be useful. Union types are a collection of two or more types which indicate that either one of those can be used.

public function foo(Foo|Bar $input): int|float;

Note that void can never be part of a union type, since it indicates “no return value at all”. Furthermore, nullable unions can be written using |null, or by using the existing ? notation:

public function foo(Foo|null $foo): void;

public function bar(?Bar $bar): void;

JIT (Just in Time compiler) rfc

The JIT — just in time — compiler promises significant performance improvements, albeit not always within the context of web requests. The JIT compiler is sort of a middle ground between compilation and interpretation. It will compile and cache some sections of code at runtime so that the compiled version can be used instead of the interpreted version. This could lead to huge performance gains for PHP, but with some caveats. Generally, JIT compilers mostly benefit CPU-intensive applications, such as 3D rendering or large mathematical computations. If you’re using PHP for web applications, you may not see a substantial performance boost by enabling the JIT compiler.

The nullsafe operator rfc

If you’re familiar with the null coalescing operator you’re already familiar with its shortcomings: it doesn’t work on method calls. Instead you need intermediate checks, or rely on optional helpers provided by some frameworks:

$startDate = $booking->getStartDate();

$dateAsString = $startDate ? $startDate->asDateTimeString() : null;

With the addition of the nullsafe operator, we can now have null coalescing-like behaviour on methods!

$dateAsString = $booking->getStartDate()?->asDateTimeString();

Named arguments rfc

Named arguments allow you to pass in values to a function, by specifying the value name, so that you don’t have to take their order into consideration, and you can also skip optional parameters!

function foo(string $a, string $b, ?string $c = null, ?string $d = null) 
{ /* … */ }

foo(
    b: 'value b', 
    a: 'value a', 
    d: 'value d',
);

Attributes rfc

Attributes, commonly known as annotations in other languages, offers a way to add meta data to classes, without having to parse docblocks. As for a quick look, here’s an example of what attributes look like, from the RFC:

use App\Attributes\ExampleAttribute;

#[ExampleAttribute]
class Foo
{
    #[ExampleAttribute]
    public const FOO = 'foo';
 
    #[ExampleAttribute]
    public $x;
 
    #[ExampleAttribute]
    public function foo(#[ExampleAttribute] $bar) { }
}
#[Attribute]
class ExampleAttribute
{
    public $value;
 
    public function __construct($value)
    {
        $this->value = $value;
    }
}

Note that this base Attribute used to be called PhpAttribute in the original RFC, but was changed with another RFC afterwards.

Match expression rfc

You could call it the big brother of the switch expression: match can return values, doesn’t require break statements, can combine conditions, uses strict type comparisons and doesn’t do any type coercion.

It looks like this:

$result = match($input) {
    0 => "hello",
    '1', '2', '3' => "world",
}; 

Constructor property promotion rfc

This RFC adds syntactic sugar to create value objects or data transfer objects. Instead of specifying class properties and a constructor for them, PHP can now combine them into one.

Instead of doing this:

class Money 
{
    public Currency $currency;
 
    public int $amount;
 
    public function __construct(
        Currency $currency,
        int $amount,
    ) {
        $this->currency = $currency;
        $this->amount = $amount;
    }
}

You can now do this:

class Money 
{
    public function __construct(
        public Currency $currency,
        public int $amount,
    ) {}
}

New static return type rfc

While it was already possible to return selfstatic wasn’t a valid return type until PHP 8. Given PHP’s dynamically typed nature, it’s a feature that will be useful to many developers.

class Foo
{
    public function test(): static
    {
        return new static();
    }
}

New mixed type rfc

Some might call it a necessary evil: the mixed type causes many to have mixed feelings. There’s a very good argument to make for it though: a missing type can mean lots of things in PHP:

  • A function returns nothing or null
  • We’re expecting one of several types
  • We’re expecting a type that can’t be type hinted in PHP

Because of the reasons above, it’s a good thing the mixed type is added. mixed itself means one of these types:

  • array
  • bool
  • callable
  • int
  • float
  • null
  • object
  • resource
  • string

Note that mixed can also be used as a parameter or property type, not just as a return type.

Also note that since mixed already includes null, it’s not allowed to make it nullable. The following will trigger an error:

// Fatal error: Mixed types cannot be nullable, null is already part of the mixed type.
function bar(): ?mixed {}

Throw expression rfc

This RFC changes throw from being a statement to being an expression, which makes it possible to throw exception in many new places:

$triggerError = fn () => throw new MyError();

$foo = $bar['offset'] ?? throw new OffsetDoesNotExist('offset');

Inheritance with private methods rfc

Previously, PHP used to apply the same inheritance checks on public, protected and private methods. In other words: private methods should follow the same method signature rules as protected and public methods. This doesn’t make sense, since private methods won’t be accessible by child classes.

This RFC changed that behaviour, so that these inheritance checks are not performed on private methods anymore. Furthermore, the use of final private function also didn’t make sense, so doing so will now trigger a warning:

Warning: Private methods cannot be final as they are never overridden by other classes

Weak maps rfc

Built upon the weakrefs RFC that was added in PHP 7.4, a WeakMap implementation is added in PHP 8. WeakMap holds references to objects, which don’t prevent those objects from being garbage collected.
Take the example of ORMs, they often implement caches which hold references to entity classes to improve the performance of relations between entities. These entity objects can not be garbage collected, as long as this cache has a reference to them, even if the cache is the only thing referencing them.

If this caching layer uses weak references and maps instead, PHP will garbage collect these objects when nothing else references them anymore. Especially in the case of ORMs, which can manage several hundreds, if not thousands of entities within a request; weak maps can offer a better, more resource friendly way of dealing with these objects.
Here’s what weak maps look like, an example from the RFC:

class Foo 
{
    private WeakMap $cache;
 
    public function getSomethingWithCaching(object $obj): object
    {
        return $this->cache[$obj]
           ??= $this->computeSomethingExpensive($obj);
    }
}

Allowing ::class on objects rfc

A small, yet useful, new feature: it’s now possible to use ::class on objects, instead of having to use get_class() on them. It works the same way as get_class().

$foo = new Foo();

var_dump($foo::class);

Non-capturing catches rfc

Whenever you wanted to catch an exception before PHP 8, you had to store it in a variable, regardless whether you used that variable or not. With non-capturing catches, you can omit the variable, so instead of this:

try {
    // Something goes wrong
} catch (MySpecialException $exception) {
    Log::error("Something went wrong");
}

You can now do this:

try {
    // Something goes wrong
} catch (MySpecialException) {
    Log::error("Something went wrong");
}

Note that it’s required to always specify the type, you’re not allowed to have an empty catch. If you want to catch all exceptions and errors, you can use Throwable as the catching type.

Trailing comma in parameter lists rfc

Already possible when calling a function, trailing comma support was still lacking in parameter lists. It’s now allowed in PHP 8, meaning you can do the following:

public function(
    string $parameterA,
    int $parameterB,
    Foo $objectfoo,
) {
    // …
}

As a sidenote: trailing commas are also supported in the use list of closures, this was an oversight and now added via a separate RFC.

Create DateTime objects from interface

You can already create a DateTime object from a DateTimeImmutable object using DateTime::createFromImmutable($immutableDateTime), but the other way around was tricky. By adding DateTime::createFromInterface() and DatetimeImmutable::createFromInterface() there’s now a generalised way to convert DateTime and DateTimeImmutable objects to each other.

DateTime::createFromInterface(DateTimeInterface $other);

DateTimeImmutable::createFromInterface(DateTimeInterface $other);

New Stringable interface rfc

The Stringable interface can be used to type hint anything that implements __toString(). Whenever a class implements __toString(), it automatically implements the interface behind the scenes and there’s no need to manually implement it.

class Foo
{
    public function __toString(): string
    {
        return 'foo';
    }
}

function bar(string|Stringable $stringable) { /* … */ }

bar(new Foo());
bar('abc');

New str_contains() function rfc

Some might say it’s long overdue, but we finally don’t have to rely on strpos() anymore to know whether a string contains another string.

Instead of doing this:

if (strpos('string with lots of words', 'words') !== false) { /* … */ }

You can now do this

if (str_contains('string with lots of words', 'words')) { /* … */ }

New str_starts_with() and str_ends_with() functions rfc

Two other ones long overdue, these two functions are now added in the core.

str_starts_with('haystack', 'hay'); // true
str_ends_with('haystack', 'stack'); // true

New fdiv() function pr

The new fdiv() function does something similar as the fmod() and intdiv() functions, which allows for division by 0. Instead of errors you’ll get INF-INF or NAN, depending on the case.

New get_debug_type() function rfc

get_debug_type() returns the type of a variable. Sounds like something gettype() would do? get_debug_type() returns more useful output for arrays, strings, anonymous classes and objects.

For example, calling gettype() on a class \Foo\Bar would return object. Using get_debug_type() will return the class name.

A full list of differences between get_debug_type() and gettype() can be found in the RFC.


New get_resource_id() function pr

Resources are special variables in PHP, referring to external resources. One example is a MySQL connection, another one a file handle.

Each one of those resources gets assigned an ID, though previously the only way to know that id was to cast the resource to int:

$resourceId = (int) $resource;

PHP 8 adds the get_resource_id() functions, making this operation more obvious and type-safe:

$resourceId = get_resource_id($resource);

Abstract methods in traits improvements rfc

Traits can specify abstract methods which must be implemented by the classes using them. There’s a caveat though: before PHP 8 the signature of these method implementations weren’t validated. The following was valid:

trait Test {
    abstract public function test(int $input): int;
}

class UsesTrait
{
    use Test;

    public function test($input)
    {
        return $input;
    }
}

PHP 8 will perform proper method signature validation when using a trait and implementing its abstract methods. This means you’ll need to write this instead:

class UsesTrait
{
    use Test;

    public function test(int $input): int
    {
        return $input;
    }
}

Object implementation of token_get_all() rfc

The token_get_all() function returns an array of values. This RFC adds a PhpToken class with a PhpToken::tokenize() method. This implementation works with objects instead of plain values. It consumes less memory and is easier to read.

Variable syntax tweaks rfc

From the RFC: “the Uniform Variable Syntax RFC resolved a number of inconsistencies in PHP’s variable syntax. This RFC intends to address a small handful of cases that were overlooked.”

Type annotations for internal functions externals

Lots of people pitched in to add proper type annotations to all internal functions. This was a long standing issue, and finally solvable with all the changes made to PHP in previous versions. This means that internal functions and methods will have complete type information in reflection.

ext-json always available rfc

Previously it was possible to compile PHP without the JSON extension enabled, this is not possible anymore. Since JSON is so widely used, it’s best developers can always rely on it being there, instead of having to ensure the extension exist first.

Breaking changes

As mentioned before: this is a major update and thus there will be breaking changes. The best thing to do is take a look at the full list of breaking changes over at the UPGRADING document. We will discuss about Breaking changes in next part.