php помогите исправить ошибку syntax error, unexpected '$this'

ошибка syntax error, unexpected '$this' (T_VARIABLE), expecting function (T_FUNCTION) or const (T_CONST) как исправить изучаю 2 день ооп.

<?php

require_once 'connect.php';

class Data{
    
    public  $login;
    public  $email;
    public  $password;
    public  $passwordConfirm; 
}


class Queries{
    public function insert(){
     
        $login = new Data();
        $email = new Data();
        $password = new Data();
        $passwordConfirm = new Data();

        $this->$login = $_POST['login'];
        $this->$email = $_POST['email'];
        $this->$password = $_POST['password'];
        $this->$passwordConfirm = $_POST['passwordConfirm'];


        $query = "INSERT INTO `users` (`login`, `email`, `password`, `passwordConfirm`) VALUES (:login, :email, :password, :passwordConfirm)";
        $params = [
            ':login' => $this->$login,
            ':email' => $this->$email,
            ':password' => $this->$password,
            ':passwordConfrim' => $this->$passwordConfirm
        ];
        $stmt = $db->prepare($query);
        $stmt->execute($params);
    }

    $this->insert();
    
}