Metaprogramming¶

Metaprogramming is the practice of writing code that treats other code as data: reading, generating, transforming, or executing programs at runtime or compile time. A metaprogram operates at a higher level of abstraction than an ordinary program because it manipulates the representation of programs rather than, or in addition to, running domain logic.

Common metaprogramming techniques include:

Reflection: inspecting types, methods, properties, or annotations at runtime, with the ReflectionClass
Code generation: emitting source files, proxy classes, or configuration from schemas, attributes, or templates
Macros: transforming code at a syntactic level before or during parsing
Eval: constructing and executing code strings at runtime
Dynamic dispatch: routing method calls through __call or __callStatic based on runtime state
Homoiconicity: using a language’s native data structures to represent and manipulate programs

PHP supports several forms of metaprogramming:

The Reflection API, with the classes ReflectionClass, ReflectionMethod, ReflectionProperty, ReflectionAttribute, provides read-only introspection of the live object model.
Magic methods, with the methods __get, __set, __call, __callStatic, __invoke, __clone, __toString, intercept property and method access at runtime.
eval() and create_function() execute dynamically constructed code strings.
nikic/php-parser enables full AST-level read and write access to PHP source from PHP itself.
PHP 8.0+ attributes allow structured metadata on declarations, consumed at runtime by frameworks and code generators.
Userland code generators, such as Doctrine proxies, Rector, Symfony DI compilation, etc. produce PHP files before or at application boot.

PHP does not support compile-time generics, hygienic macros, metaclasses, or a Meta-object Protocol: the object model is implemented in C and is not programmable from userland.

<?php

    // 1. Reflection: introspect a class at runtime
    $rc = new ReflectionClass(ArrayObject::class);
    echo $rc->getMethod('offsetGet')->getNumberOfParameters(); // 1

    // 2. Dynamic dispatch via magic method
    class DynamicProxy {
        public function __call(string $name, array $args): mixed {
            return strtoupper($name) . '(' . implode(', ', $args) . ')';
        }
    }
    echo (new DynamicProxy())->hello('world'); // HELLO(world)

    // 3. Attribute-driven metadata (PHP 8.0+)
    #[\Attribute(\Attribute::TARGET_METHOD)]
    final class Route {
        public function __construct(public readonly string $path) {}
    }

    class UserController {
        #[Route('/users')]
        public function index(): void {}
    }

    $attr = (new ReflectionMethod(UserController::class, 'index'))
        ->getAttributes(Route::class)[0]
        ->newInstance();
    echo $attr->path; // '/users'

?>

Documentation

Metaprogramming¶

PHP Dictionary

Navigation

Related Topics