what is new in PHP 8.0

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 that 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 rfc

The JIT — just in time — compiler promises significant performance improvements, albeit not always within the context of web requests. I’ve done my own benchmarks on real-life web applications, and it seems like the JIT doesn’t make that much of a difference, if any, on those kinds of PHP projects.

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. If you want to take a deep dive in how attributes work, and how you can build your own; you can read about attributes in depth on this blog.

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,
    ) {}
}

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 that 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);
    }
}

Mustafa's zettelkasten 📔

Explorer