Why does this not make a difference between property and variable?

Question

class someclass
{
    public $foo = \'abcd\';

    public function __construct($data)
    {
        $this->foo = $data;
    }
    public function doSomething()
    {
         


        

Answer 1

change this

echo $foo = $_POST['foo'];

to

echo $this->foo = $_POST['foo'];
var_dump($this->foo);