RFC Proposal: Readonly Structs in PHP

Dear PHP Internals, I am writing to propose a new feature for PHP that introduces the concept of structs. This feature aims to provide a more concise and expressive way to define and work with immutable data structures. Below is a detailed description of the proposed syntax, usage, and behavior. Syntax struct Data {

    string $title;
    Status $status;
    ?DateTimeImmutable $publishedAt = null;

} The Data struct is essentially represented as a readonly class with a constructor as follows: readonly class Data {

    public function __construct(
        public string $title,
        public Status $status,
        public ?DateTimeImmutable $publishedAt = null,
    ) {}

} Assertions The Data struct will always be readonly. It has no methods besides the constructor. Constructors The Data struct can be constructed in three different ways, each of which allows for named or positional arguments, which can be mixed: 1.1 Class like $data = new Data('title', Status::PUBLISHED, new DateTimeImmutable()); 1.2 Class like (Named Syntax) $data = new Data(title: 'title', status: Status::PUBLISHED, publishedAt: new DateTimeImmutable()); 2.1 Proposed struct initialization syntax (Positional Arguments) $data = Data{'title', Status::PUBLISHED, new DateTimeImmutable()}; 2.2 Proposed struct initialization syntax (Named Syntax) $data = Data{title: 'title', status: Status::PUBLISHED, publishedAt: new DateTimeImmutable()}; 3.1 Anonymous Struct (Named Arguments) $data = struct {

    string $title;
    Status $status;
    ?DateTimeImmutable $publishedAt = null;

}('title', Status::PUBLISHED, new DateTimeImmutable()); 3.2 Anonymous Struct (Named Arguments - Named Syntax) $data = struct {

    string $title;
    Status $status;
    ?DateTimeImmutable $publishedAt = null;
}(title: 'title', status: Status::PUBLISHED, publishedAt: new DateTimeImmutable());

Nesting The proposed feature also supports nesting of structs. For example: final class HasNestedStruct {

    NestedStruct {
        string $title;
        Status $status;
        ?DateTimeImmutable $publishedAt = null;
    };

    public function __construct(
        public string $string,
        public Data $normalStruct,
        public NestedStruct $nestedStruct = NestedStruct{'title', Status::PUBLISHED, new DateTimeImmutable()},
        public struct InlineNamed { int $x} $inlineNamed = {x: 1},
        public { int $x, int $y} $inlineAnonymous = {x: 1, y: 2},
    ) {}

} This proposal aims to enhance the readability and maintainability of code by providing a more concise and expressive way to work with immutable data structures in PHP. I believe this feature will be a valuable addition to the language as it not only opens the door for future enhancements (eg. typed json deserialization, etc.), but should also help reduce reliance on arrays by providing a more expressive alternative. Your feedback and suggestions are highly appreciated, and we look forward to discussing this proposal further within the PHP internals community. Sincerely Lanre