How to acces ouside variable value in abstract call in PHP : i am new in PHP. I tired to access outside variable values in Abstract class. The code written blow. Help to fix it. I think i am doing something wrong But i don't know. 

    <?php
        $a = "value1";
        $b = "value2";
        abstract class connect {
            
            public function __construct() {
              $sum = $a + $b;
               return $sum;
              }
        }
    ?>