<?php
class a {
    public $attr = 'a';
    
    public $x = 'q';
}

class b extends a { 
    public $abc = 'b';
    public $attr = 'bc';    
    
    public function getVar($var){
        $reflect = new ReflectionObject($this);
        $properties = (array)$reflect->getProperties();
        $parent = $reflect->getParentClass();
        
        $parent_reflect = new ReflectionObject(new $parent->name());
        $parent_properties = $parent_reflect->getProperties();
        if($reflect){
            foreach($properties as $property){
                foreach($parent_properties as $parent_property){
                    if($property->name == $var && $property->class == $reflect->getName() && $parent_property->name == $var){
                        trigger_error($var . ' is finnal property');
                        return false;
                    }
                }
            }
        }
        
        if(!$reflect->hasProperty($var)){
            trigger_error('Undefined property:' . $var);
        }else{
            return $this->$var;
        }
    }
}

$a = new b();
echo $a->getVar('attr');