test

show code

<?php
    $someGlobalVar = "test";
    class myClassTest
    {       
        public $var1;
        public $var2;
        public $var3;
    
        function __construct($arg1,$arg2=null){
            if ($arg2 === null){
                global $someGlobalVar;
                $arg2 = $someGlobalVar;
            }
            echo $arg2;
            $this->var1 = $arg1;
            $this->var2 = $arg2;
            $this->var3 = array();
        }
     }
     $class = new myClassTest('something'); //outputs test