PHP enums are the modern, safer alternative to traditional constant groups. 1. They provide type safety, preventing invalid values. 2. They enable IDE autocompletion and better tooling support. 3. They are first-class types usable in type hints and instanceof checks. 4. They allow iteration via cases(). 5. They support methods and behavior on cases. Backed enums map to scalar values, while pure enums represent identity. Migrate when you have fixed sets of options, use strings/integers for states, or need better type safety and tooling. Enums are a fundamental upgrade over constant groups and should be used for new code in PHP 8.1 .

PHP enums are indeed the modern, more robust alternative to traditional constant groups — a shift that brings PHP in line with other modern programming languages. If you’ve been using class constants or global constants to represent fixed sets of values (like status codes, user roles, or order states), enums offer a cleaner, safer, and more expressive way to do it.

Let’s break down why enums are considered the successor and how they improve upon the old ways.

Why Traditional Constant Groups Fall Short

Before PHP 8.1 introduced enums, developers often used class constants to simulate enumerated types:

class OrderStatus
{
    const PENDING = 'pending';
    const SHIPPED = 'shipped';
    const DELIVERED = 'delivered';
}

Or sometimes with a list of global constants:

define('STATUS_PENDING', 'pending');
define('STATUS_SHIPPED', 'shipped');
// ...

These approaches have several issues:

• ? No type safety — nothing stops you from passing 'cancelled' (misspelled) or even an integer.
• ? No autocompletion or IDE support beyond basic constant lookup.
• ? No way to iterate over the possible values.
• ? No distinction between the constant name and its value — they’re loosely coupled.

You could work around some of these with helper methods, but it’s boilerplate-heavy and error-prone.

Enums Bring Type Safety and Clarity

With PHP enums (backed or pure), you define a closed set of allowed values, and the type system enforces it.

Basic Enum Example

enum OrderStatus: string
{
    case PENDING = 'pending';
    case SHIPPED = 'shipped';
    case DELIVERED = 'delivered';
}

Now you can type-hint parameters:

function updateStatus(OrderStatus $status): void
{
    // $status is guaranteed to be one of the three cases
}

This prevents bugs from invalid strings or wrong types being passed in.

Key Advantages of Enums Over Constant Groups

? 1. Type Safety

You can’t accidentally pass 'Pendng' or null where an OrderStatus is expected (if properly type-checked).

? 2. Autocompletion & Tooling Support

IDEs can suggest valid enum cases, reducing typos and improving developer experience.

? 3. First-Class Citizens

Enums are real types. You can use them in type hints, instanceof checks, and even serialize/deserialize safely.

? 4. Iteration

You can loop over all cases:

foreach (OrderStatus::cases() as $case) {
    echo $case->value . "\n";
}

This is impossible with plain constants without manual arrays.

? 5. Methods and Logic

You can add methods to enums:

enum OrderStatus: string
{
    case PENDING = 'pending';
    case SHIPPED = 'shipped';
    case DELIVERED = 'delivered';

    public function isFinal(): bool
    {
        return $this === self::DELIVERED;
    }
}

Now each case carries behavior, not just data.

Backed vs Pure Enums

PHP supports both:

• Backed enums have a scalar value (string or int), useful when mapping to database values.
• Pure enums don’t need a backing value and are used when only the identity of the case matters.

// Backed
enum UserRole: string
{
    case ADMIN = 'admin';
    case USER = 'user';
}

// Pure
enum HttpStatus
{
    case OK;
    case NOT_FOUND;
    case SERVER_ERROR;
}

Pure enums are great for state machines or flags where the label is the thing.

When Should You Migrate?

You don’t need to rewrite all your constants tomorrow, but for new code or critical domains (like statuses, permissions, states), enums are the better choice.

Consider switching when:

• You have a fixed, known set of options.
• You’re using strings or integers to represent states.
• You’re doing string comparisons like if ($status === 'pending').
• You want better type safety and IDE support.

Bottom Line

PHP enums aren’t just syntactic sugar — they’re a fundamental upgrade over constant groups. They give you type safety, better tooling, iteration, and the ability to attach logic to your constants.

If you're on PHP 8.1 , there’s little reason to keep using class constants for enumerated values. Enums are the modern, safer, and more expressive way.

Basically, if you're still defining const groups for statuses or types, it's time to level up.

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