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Amit Merchant

Amit Merchant

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Native enumerations (enums) are coming in PHP 8.1

Enums or enumerations or enumerator types are those little data structures that can be used to define a set of named values. More like constants. For instance, a contract status which can be “permanent”, “temp”, or “apprentice”. Or a order status that can be “ordered”, “dispatched”, “shipped” etc.

You can use an Enum to represent a smallish fixed set of constants or an internal class mode while increasing readability.

Languages like Java, C, TypeScript has enums for quite some time now. For instance, if you want to define an enum data type in Java, you can do it like so.

enum Cardsuit { 
Cardsuit trump;

PHP didn’t have a true native implementation of enums. There are libraries out there such as Sptie’s enum which somewhat fill this gap. These libraries make use of classes and DocBlock to replicate the behavior of enums.

But as I said earlier, the native implementation was still missing. And that’s where PHP 8.1 comes into play which tries to bring in native enums in PHP.

Enums in PHP 8.1

If you look at the recent RFCs for PHP 8.1, it seems like the native enumerations are coming in the upcoming version of PHP. While the RFC is still in the voting phase, if you check the number of approved votes it has got, it’s pretty evident that it will surely make its way into PHP 8.1.

The RFC I’m talking about is proposed for the target version of PHP 8.1.

Essentially, this PR introduces a new language construct called enum. There could be two types of enums.

  • Basic/pure enums
  • Backed enums

Basic/pure enums

A basic enum is the enums whose enumerated cases don’t have scalar types. They are simply singleton objects. Here’s how an example basic/pure enum would look like.

enum OrderStatus 
  case Completed;
  case Dispatched;
  case Shipped;
  case Cancelled;

As you can tell,

  • A basic enum can be declared using the enum keyword followed by the enum name that you want to specify. In this example, it’s OrderStatus.

  • Inside the enum, you can specify a fixed set of legal values that an enum can hold using the keyword case followed by the value. In this example, OrderStatus::Completed, OrderStatus::Dispatched, OrderStatus::Shipped, and OrderStatus::Cancelled are the only fixed set of values that the OrderStatus enum holds.

  • Enums can be autoloaded the same way classes, interfaces, and traits are autoloaded. So, if we want to declare the previous enum under a namespace, you can do it like so.

namespace App\Enums;

enum OrderStatus 
  case Completed;
  case Dispatched;
  case Shipped;
  case Cancelled;

And you can import it like so.

use App\Enums\OrderStatus;
  • An Enumeration may have zero or more case definitions, with no maximum.

  • All Cases have a read-only property, name, that is the case-sensitive name of the case itself which can be accessed like so.

print OrderStatus::Completed->name;
// prints "Completed"

Backed Enums

Backed enums are those enums where you can assign scalar values of type int or string to the enumerated cases. Here’s an example backed enum.

enum OrderStatus: string 
  case Completed = 'completed';
  case Dispatched = 'dispatched';
  case Shipped = 'shipped';
  case Cancelled = 'cancelled';

As you can see, you can “back” enumeration cases using int or string values. Hence, it’s called “Backed enums”.

A few things to note here is, when you back enumeration cases, you would need to be consistent. Meaning, if you’re backing cases with int values, all cases in the enum should be backed by int values. You can not mix int and string in a single backed enumeration.

So, this means you need to type-hint the enum with the type (int, string, and so on) that you want to back it with.

Second important thing is, when you back enum cases, all the enumeration cases should be backed. You can not have pure and backed enumerated cases altogether.

You can access the case values using a read-only property called value like so.

print OrderStatus::Cancelled->value;

// prints "cancelled"

Fetch Enum Cases

You can fetch all the enum cases of Pure and Backed enums by calling a static method on the enum called cases() because both these enum types implement an internal interface named UnitEnum.

The method returns a packed array of all defined Cases in the order of declaration like so.



Advantage of using enums

Enums can be useful on various occasions. For instance, you can type-check a function against an enumerated type, in which case only values of that type may be passed like so.

use App\Enums\OrderStatus;

function setOrderStatus(OrderStatus $status) {...}

setOrderStatus('Shipped'); // TypeError: setOrderStatus(): Argument #1 ($status) must be of type OrderStatus, string given

setOrderStatus(OrderStatus::Shipped); // Passes

On top of this, when used properly, enums can drastically improve code correctness and readability.

In Closing

So, that was a brief introduction to Enums in PHP 8.1. But there is more to it. It was just the tip of the iceberg. There are a few other things that you can do with enums such as use methods (generic and static), constants, traits right within enums which I haven’t covered in this article.

You can learn more about Enums here at the official RFC.

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