Readonly Classes and Properties in

About Readonly Classes and Properties

Readonly classes and properties allow classes to specify public properties for easy access but prevent modification. To declare a property as readonly, it must have readonly added before the type specification. The property is allowed to be assigned once, but any attempt to re-assign or modify the value will result in an Error.

<?php

class Block
{
    public function __construct(
        public readonly int $length,
        public readonly int $width,
    ) {
    }
}

Readonly classes build on this behaviour which, if declared as readonly, apply the read only declaration to each property. Additionally it prevents the addition of dynamic properties.

<?php

readonly class Block
{
    public function __construct(
        public int $length,
        public int $width,
    ) {
    }
}