PHP Metaprogramming refers to writing code that can generate or manipulate other code. In other words, it allows programs to have greater flexibility by enabling them to inspect, modify, or even generate new code at runtime. It can also involve techniques like reflection, dynamic code generation, and introspection.
In PHP, metaprogramming is most commonly done using:
Let's demonstrate metaprogramming in PHP using the Reflection API and Magic Methods.
Here, we'll create a class that uses magic methods (__get and __set) to handle non-existent properties dynamically.
<?php class DynamicClass { private $data = []; // Magic method to handle dynamic property setting public function __set($name, $value) { echo "Setting '$name' to '$value'.\n"; $this->data[$name] = $value; } // Magic method to handle dynamic property getting public function __get($name) { if (array_key_exists($name, $this->data)) { echo "Getting '$name'.\n"; return $this->data[$name]; } echo "Property '$name' not set.\n"; return null; } // Magic method to handle dynamic method calls public function __call($name, $arguments) { echo "Calling method '$name' with arguments: " . implode(', ', $arguments) . "\n"; return null; } } // Usage example $obj = new DynamicClass(); // Setting properties dynamically $obj->name = "Metaprogramming"; $obj->type = "PHP"; // Getting properties dynamically echo $obj->name . "\n"; // Outputs: Metaprogramming echo $obj->type . "\n"; // Outputs: PHP // Calling a dynamic method $obj->dynamicMethod("arg1", "arg2");
Output:
Setting 'name' to 'Metaprogramming'. Setting 'type' to 'PHP'. Getting 'name'. Metaprogramming Getting 'type'. PHP Calling method 'dynamicMethod' with arguments: arg1, arg2
PHP’s Reflection API allows inspecting and manipulating classes, methods, and properties at runtime.
<?php class ExampleClass { public $name; public $type; public function __construct($name, $type) { $this->name = $name; $this->type = $type; } public function sayHello() { echo "Hello from $this->name, a $this->type example!\n"; } } function reflectOnClass($className) { // Reflecting on the class $reflector = new ReflectionClass($className); echo "Class: " . $reflector->getName() . "\n"; // Reflecting on the class properties echo "Properties: \n"; foreach ($reflector->getProperties() as $property) { echo "- " . $property->getName() . "\n"; } // Reflecting on the class methods echo "Methods: \n"; foreach ($reflector->getMethods() as $method) { echo "- " . $method->getName() . "\n"; } } // Usage example $example = new ExampleClass("Metaprogramming", "PHP"); $example->sayHello(); // Outputs: Hello from Metaprogramming, a PHP example! // Reflecting on the ExampleClass reflectOnClass('ExampleClass');
Output:
Hello from Metaprogramming, a PHP example! Class: ExampleClass Properties: - name - type Methods: - __construct - sayHello
Now let’s build a metaprogramming example where we invoke methods dynamically on an object using the ReflectionMethod class.
<?php class Calculator { public function add($a, $b) { return $a + $b; } public function multiply($a, $b) { return $a * $b; } } function dynamicInvoke($object, $methodName, $args) { try { $method = new ReflectionMethod($object, $methodName); return $method->invokeArgs($object, $args); } catch (ReflectionException $e) { echo "Method not found: " . $e->getMessage() . "\n"; } } // Example usage $calc = new Calculator(); // Dynamically invoke 'add' method $result1 = dynamicInvoke($calc, 'add', [2, 3]); echo "Addition Result: " . $result1 . "\n"; // Outputs: 5 // Dynamically invoke 'multiply' method $result2 = dynamicInvoke($calc, 'multiply', [3, 4]); echo "Multiplication Result: " . $result2 . "\n"; // Outputs: 12 // Attempt to invoke a non-existent method dynamicInvoke($calc, 'subtract', [5, 2]);
Output:
Addition Result: 5 Multiplication Result: 12 Method not found: Method Calculator::subtract() does not exist
Metaprogramming in PHP is a powerful technique that enables developers to write flexible and dynamic code. Using the Reflection API, magic methods, and other tools like closures or eval, PHP metaprogramming provides the ability to introspect and manipulate the structure and behavior of objects and methods at runtime. However, it should be used cautiously, especially when security is a concern.
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