问为什么在使用继承的类中没有设置这个变量？

EN

<?php 
session_start();
class validation{
    public $user_data; #storing users data
    public $errors; #storing errors that occurs

    #this function takes users data as an associative array and store it in class $user_data property
    public function __construct($data)
    {
        $this->user_data = $data;
        
        #searching for any empty user inputs
        foreach($this->user_data as $key => $value){
            if(empty($value)){
                #using session variables to display errors to users
                $_SESSION["$key"."_empty"] = "set";
                #storing the errors in $errors property of this class
                $this->errors[] = "empty $key"; 
            }else{
                unset($_SESSION["$key"."_empty"]);
            }
        }
        #using session variables to hold data in the text-box
        foreach($this->user_data as $key => $value){
            $_SESSION["$key" . "_value"] = $value;
        }
    }
}  

#real problem starts from here, the errors are not storing  
class email_validate extends validation{
    function __construct(){
        if(!filter_var($this->user_data['email'], FILTER_VALIDATE_EMAIL)){
            $this->errors[] = "inval email";
            $_SESSION['inval email'] = 'set';
        }else{
            unset($_SESSION['inval email']);
        }
    }
}
class password_validate extends validation{
    function __construct(){
        if(strlen($this->user_data['password']) < 6){
            $this->errors[] = "inval password";
            $_SESSION['inval password'] = 'set';
        }else{
            unset($_SESSION['inval password']);
        }
    }
}
#here is an other problem in this class
class repeat_password_validate extends validation{
    function __construct(){
        if($this->user_data['password'] !== $this->user_data['reppassword']){
            $this->errors[] = "inval repeat password";
            #this session is not getting set
            $_SESSION['inval rep password'] = 'set';
        }else{
            unset($_SESSION['inval rep password']);
        }
    }
}



$data = array("email" => "{$_POST['email']}", "password" => "{$_POST['password']}", "reppassword" => "{$_POST['reppassword']}");
$validation = new validation($data);

#executing validation
$email = new email_validate();
$password = new password_validate();
$repeated_password = new repeat_password_validate();
       

echo "<pre>";
print_r($validation->errors);
?>