How To Dynamically Instantiate Classes In PHP
Posted on March 10th, 2009 in Annabel, Work | 2 Comments »
For Annabel, I need to be able to dynamically instantiate classes, based on options in a configuration file (Zend_Config_Ini). However, some of these classes have constructors (some with required options), others don’t even have a constructor. I first tried to instantiate them with call_user_func_array, like this:
$datatype_options = explode(',', $global_config->customer->data->field->$key->type);
$datatype_class = array_shift($datatype_options);
$class = call_user_func_array(array($datatype_class, '__construct'), $datatype_options);
This didn’t work, since some classes don’t have a constructor and they were not static. Then, I came up with another solution: use a generic static method getInstance() to do it, like this:
class Test {
public static function getInstance($classname)
{
return new $classname();
}
}
$datatype_options = explode(',', $global_config->customer->data->field->$key->type);
$datatype_class = array_shift($datatype_options);
$class = call_user_func_array(array('Test', 'getInstance'), $datatype_options);
This worked, as long as I don’t need any constructor parameters. But for some classes, I do need them. So I went thinking, and came to the conclusion that I would need the Reflection API to do what I want. Finally, I implemented the following solution, which works perfectly. It could probably be cleaned up a little bit, but it basically works:
class Annabel_Data
{
/**
* Creates instances of classes in the Annabel_Data package.
*
* To use this, provide arguments in the order you would need them
* in the instantiated classes, with as the first argument the name
* of the class to instantiate.
*
* @param $arguments An array with arguments
*
* @return Annabel_Data_Abstract
*/
public static function factory($arguments)
{
$class_name = array_shift($arguments);
$class_name = 'Annabel_Data_' . ucfirst($class_name);
Zend_Loader::loadClass($class_name);
$reflector = new ReflectionClass($class_name);
if ($reflector->isInstantiable()) {
$constructor = $reflector->getConstructor();
if (is_null($constructor)) {
return $reflector->newInstance();
}
$params = $constructor->getNumberOfParameters();
$req_params = $constructor->getNumberOfRequiredParameters();
if (count($arguments) < $req_params) {
throw new Annabel_Data_Exception('Please provide ' . $req_params . ' parameters to instantiate class ' . $class_name);
}
if (0 < $params) {
return $reflector->newInstanceArgs($arguments);
} else {
return $reflector->newInstance();
}
} else {
throw new Annabel_Data_Exception("Could not instantiate a class of type '" . $class_name . "'");
}
}
}
$datatype_options = explode(',', $global_config->customer->data->field->$key->type);
$class = Annabel_Data::factory($datatype_options);
This works perfectly, for each case I need it (and tested it 
). I should add some more exception checking and things like that, but those are minor details.
Oh, and last but not least, some credits go the commenters over at the PHP Reflection API documentation.