Question

class A {}
class B extends A {}
class C extends A {}
class D extends C {}

$class="C";
if ($class instanceof A) {  //This is just for demonstration - I know instanceof won't work!!!
   $object=new $class("","",1)
}

How can a check the string “C” to check that this classname is a child of A?

I looked into is_a() but it doesn’t help.

I am specifically asking for “C” as I am getting the class name dynamically and I can’t instantiate without knowing what parameters to pass to constructor!

Answer 1

You can use PHP’s reflection class to look at class inheritance given a string name. For example, you could easily build an array of all parent classes like this:

$class = new ReflectionClass('whatever');

$parents = array();
$current_class = $class;
while ($current_class = $current_class->getParentClass()) {
    $parents[] = $current_class->getName();
}
var_dump($parents);

Of course you may find this more troublesome than you instantiating an object an using instanceof.

The ReflectionClass also has a lot of other interesting methods that might help you since it seems you are interested in finding out properties of a class just given it’s name.

Check the link for more info:

http://php.net/manual/en/class.reflectionclass.php

For example, you could get the information on parameters needed for the current class’ constructor like this:

$class = new ReflectionClass('whatever');
$const_params = $class->getConstructor()->getParameters();
var_dump($const_params);