PHP 8.1 Changes

PHP 8.1 added enums, readonly properties, intersection types, first-class callable syntax, Fibers, and the never return type. Enums and readonly properties are the changes most likely to improve ordinary domain code.

Changes Worth Recognising

• Backed enums model a closed set while still mapping to stored strings or integers.
• Readonly properties can be assigned once from class scope.
• Intersection types require a value to satisfy every listed interface.
• First-class callable syntax such as trim(...) creates a Closure.

Representative Code

<?php

enum OrderStatus: string
{
    case Draft = 'draft';
    case Paid = 'paid';
}

echo OrderStatus::Paid->value . PHP_EOL;

// Prints:
// paid

Upgrade Review

• Decide how unknown stored enum values are handled during hydration.
• Do not confuse readonly properties with deeply immutable objects.
• Adopt Fibers through a library abstraction unless you are building infrastructure.

Enums can remove repeated string validation, but database and API boundaries still need explicit conversion and failure handling.