Dynamic Properties in PHP and StdClass

Languages like JavaScript and Python allow object instances to have dynamic properties. As it turns out, PHP does too. Looking at the official PHP documentation on objects and classes you might be lead to believe dynamic instance properties require custom __get and __set magic methods. They don't.

Simple, Built-in Dynamic Properties

Check out the following code listing:

class DynamicProperties { }
$object = new DynamicProperties;
print isset($object->foo) ? 't' : 'f'; // f

// Set Dynamic Properties foo and fooz
$object->foo = 'bar';
$object->fooz = 'baz';

// Isset and Unset work
isset($object->foo); // true
unset($object->foo);

// Iterate through Properties and Values
foreach($object as $property => $value)  { 
     print($property . ' = ' . $value . '<br />'); 
}

// Prints:
//   fooz = baz

Using the built-in dynamic instance properties is an order of magnitude faster (30x, by my profiling) than using magic __get and __set methods. Built in dynamic property accesses happen without invoking a method call back to PHP script.

So when does it make sense to use __get and __set? If you need more complex behavior, like calculated properties, you must use __get and __set. Also, as an astute comment points out, if you would prefer not to have dynamic properties on a class you can throw errors from __get and __set.

StdClass: Anonymous Objects

Sometimes all that is necessary is a property bag to throw key value pairs into. One way is to use array, but this requires quoting all keys. Another way is to use dynamic properties on an instance of StdClass. StdClass is a sparsely documented class in PHP which has no predefined members.

$object = new StdClass;
$object->foo = 'bar';
json_encode($object);

Next I'll touch on the SPL's Countable and ArrayAccess as a means of being able to accomplish the following in PHP:

class MyClass implements Countable, ArrayAccess { ... }
$myObject = new MyClass();
// Using array access notation
$myObject[0] = 'hello';
$myObject[1] = 'world';
$myObject['foo'] = 'bar';

Thanks to the folks pointing out that you don't need to extend from StdClass in order to have dynamic properties!