PHP 8.2 introduced read-only classes. In PHP 8.1, you can already define read-only properties that cannot be overwritten from outside.
Now, you can automatically declare all class properties as readonly. All the previous rules (read-only properties) will apply.
Hum, why making all properties read-only?
To prevent dynamic properties (deprecated), even with the special attribute #[AllowDynamicProperties], for example.
PHP 8.2 syntax for read-only classes
readonly class Test {
public string $property;
}
You can't use it for everything
Unless it's a standard class or an abstract, you cannot use the readonly keyword with the following structures:
- Interfaces
- Enums
- Traits
You would get a fatal error.
Type safety vs. immutability
Whether it's for read-only properties or entire read-only classes, you can only use the readonly keyword with typed properties.
You also cannot circumvent this mechanism with inheritance. Child classes will have to be read-only too.
However, read-only does not mean immutable, as if your properties hold objects, these objects can still change. It's essential to keep that in mind.
Wrap up
The classic usage would be for object values. You write less code, but it does not guarantee immutability everywhere.
Top comments (2)
wiki.php.net/rfc/readonly_amendments : although, it will be possible to extend read-only classes with "non read-only" classes in PHP 8.3
It seems that some advanced features you might need, like deep clone, do not work properly for now.
Great article. When I first read about readonly classes/properties, I was very excited, but I some how missed the change that is happening in 8.3. I think the change makes sense.