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generics-rfc.md

Title: Generic Types and Type Parameters in PHP

• Version: 1.0
• RFC Type: Feature
• Author: Your Name
• Status: Draft

Introduction

The purpose of this RFC is to propose the addition of generic types and type parameters to the PHP language. Generics provide a powerful mechanism for writing reusable and type-safe code by allowing the definition of generic classes, interfaces, and functions that can operate on a variety of types.

Motivation

Currently, PHP does not have built-in support for generics, which limits the ability to write reusable and type-safe code. With the increasing complexity of modern PHP applications, the addition of generics would provide a significant improvement in code quality and maintainability.

Proposal

1. Syntax for Generic Types and Type Parameters: The proposal introduces the use of angle brackets (<>) to denote generic types and type parameters. Type parameters are specified when declaring a generic class, interface, or function, allowing the code to operate on different types.

2. Declaring Generic Classes: A class can be declared as generic by specifying one or more type parameters in angle brackets after the class name. For example:

   <?php
   class Collection<T> {
       // class implementation
   }

3. Using Generic Types: Generic types can be used in properties, method return types, and method parameter types. For example:

   <?php
   class Collection<T> {
       private array $items = [];
   
       public function addItem(T $item): void {
           // method implementation
       }
   
       public function getItem(): T {
           // method implementation
       }
   }

4. Declaring Generic Interfaces: Interfaces can also be declared as generic, allowing the specification of type parameters that can be used by implementing classes. For example:

   <?php
   interface Iterator<T> {
       public function next(): T;
   }

5. Implementing Generic Interfaces: When implementing a generic interface, the implementing class can either specify concrete types for the type parameters or rely on type inference. For example:

   <?php
   class StringIterator implements Iterator<string> {
       // implementation
   }

6. Using Generic Functions: Generic functions can be declared by specifying type parameters before the function name. The type parameters can then be used in the function's return type and parameter types. For example:

   <?php
   function reverse<T>(array $input): array {
       // function implementation
   }

Compatibility

The introduction of generics will not break backward compatibility with existing PHP code. Existing codebases will continue to function as before, and generics will be an opt-in feature.

Proposed PHP Version

This feature is proposed for inclusion in PHP 9.

Conclusion

The addition of generics to PHP would bring significant benefits to the language by enabling the creation of more reusable, type-safe, and maintainable code. It would provide developers with a powerful tool to write generic classes, interfaces, and functions that can operate on a variety of types.