Reflections: Unsung Hero's of PHP

What are Reflections?

First off, if you don't know what Reflections are, you should take a quick walk through the PHP: Reflection manual. You have been missing out. Reflections are some of the most powerful shadow features in current generation ( >= PHP5.3).

PHP 5.3 comes with a complete reflection API that adds the ability to reverse-engineer classes, interfaces, functions, methods and extensions. Many PHP developers are familiar with call_user_func_array(), but not Reflections. This function allows you to pass arguments to an object of the Callable type, most commonly a function or class method. It was introduced in 4.0.4 and gave developers a new approach to dynamically constructing code. Here is an example to freshen your memories:

// Example function function 
example($arg1, $arg2){ 
    echo $arg1; // Prints: argument_a 
    echo $arg2; // Prints: argument_b 
} 


// array with contents to be passed to function 
$arguments = array("argument_a", "argument_b"); 


// pass argument array to function example 
call_user_func_array('example', arguments);

This may not seem like a big deal, but in some scenarios, you can't always estimate where you get your arguments from (although some will argue this is bad coding practice). If you have a string, like "this|is|a|string", you can explode it and pass the parts to call_user_func_array(). The string can then be any number of parts long, and if you want, you could catch them in the example() function using func_get_args().

What can Reflections do?

Reflections are very powerful, in many ways. They give a developer the ability to read document comments, dynamically call methods, invoke arguments and more. It takes the ability that call_user_func_array(), and allows you to extend it even further.

Here is a simple example using a sample class:

// Example Class
class ExampleClassToReflect { 
    private $classData; 


    public function __construct($arg1, $arg2){ 
        // Construct Called 
        $this->classData = "$arg1 reflected $arg2\n"; 
    } 


    public function callMethod(){ return $this->classData; } 
} 


$rc = new ReflectionClass('ExampleClassToReflect'); 
$class = $rc->newInstanceArgs(array('foo', 'bar')); 
echo $class->callMethod(); // returns 'foo reflected bar'

The above will create an instance of ExampleClassToReflect and pass the arguments foo and bar to it's constructor. You can then use the variable $class just as if you called the class using the new keyword.

Conclusion

Staying up on new functions and classes is very important. There are a lot of snippets of [>= PHP5.3] code I have seen where someone uses an eval() but had they known about Reflections, they could have saved themselves both headache and vulnerability exposure.