Question

I need to get all declared classes which are have extended another parent class.

So for example…

class ParentClass {

}

class ChildOne extends ParentClass {

}

class ChildTwo extends ParentClass {

}

class ChildThree {

}

I need an array that outputs this:

array('ChildOne', 'ChildTwo')

I’m new to PHP OOP, but based on some Googling, I came up with this solution.

$classes = array();

foreach( get_declared_classes() as $class ) {
    if ( is_subclass_of($class, 'ParentClass') ){
        array_push($classes, $class);
    }
}

What I want to ask is whether this is the best practice to do what I want to do, or is there a better way? The global scope will contain a lot of other classes that isn’t a child of ParentClass. Is looping through all declared classes the best way to go?

EDIT (clarification of purpose):

What I want to achieve with this is to instantiate each child class extending the parent class.

I want to do $childone = new ChildOne; $childtwo = new ChildTwo; for every child of ParentClass.

Answer 1

Your solution seems fine, though I’m not sure why you’d do this. There is no easy way in php to say, ‘give me all the declared classes of a certain parent class globally’ without actually checking globally each declared class. Even if you have a couple hundred classes loaded to loop through, it shouldn’t be too heavy as they’re all in memory.

If you’re trying to just track loaded child classes for a specific parent, why not create a registry that tracks them when they’re loaded? You could do this tracking in an autoloader or factory used for the child classes or event as a hack, just by putting something at the top of the class file before the class definition.