PHP 8.2 introduces read-only classes

A major update to the stalwart scripting language for web development, PHP 8.2 has arrived with performance, syntax, and type safety improvements along with new capabilities such as read-only classes and stand-alone types.

PHP 8.2 was published December 8 and can be accessed from php.net.

Support for read-only classes in PHP 8.2 means that a class marked with the readonly modifier will mark all instance properties of the class as read-only and prevent the creation of dynamic properties. Marking readonly classes with the AllowDynamicProperties attribute triggers a compile error.

The addition of null, false, and true as stand-alone types in PHP 8.2 is described as a “programming enhancement.” The null type corresponds to PHP’s unit type (the type that holds a single value) while false and true are literal types of type bool. These changes promote type system completeness and serve a number of edge cases.

In other improvements in PHP 8.2:

• Disjunctive normal form (DNF) types enable the combination of union and intersection types, following a strict rule that says when combining union and intersection types, intersection types must be grouped with brackets.
• A “random” extension provides an object-oriented API to random number generation.
• The creation of dynamic properties has been deprecated, to help avoid mistakes and typos, unless the class opts in by using the AllowDynamicProperties attribute; stdclass allows dynamic properties.
• New classes, interfaces, and functions are featured, such as a msqli_execute_query function and a SensitiveParameter attribute.
• Constants now can be defined in traits.
• The ${} string interpolation has been deprecated.

PHP 8.1, which featured new capabilities regarding enums, syntax, and read-only properties, arrived in November 2021. It was followed by several point releases.