为什么我的getter（__get）没有在PHP类中调用？

Question

I have read all related question, but failed to remove the bug from my code. Please guide me about possible error in my code. When I try to call following code, it reports Error: Call to undefined method SessionManager::close() in E:\wamp64\www\mjs-cms\private\systemcore\helper\SessionManager.php on line 22 instead of "tried to call close".

Thanks in advance.

<?php
defined('BASEPATH') OR exit('No direct script access allowed');
class SessionManager{
    public function __construct() {
        session_start();
    }
    public function is_exist($a){
        return isset($_SESSION["system".$a]);
    }

    public function add($a,$b){
        $_SESSION["system".$a]=$b;
    }
    public function  addCookies($a,$b){
        setcookie($a, $b, time() + (86400 * 30), "/"); // 86400 = 1 day
    }
    public function sessionKey(){
        return session_id();
    }
    public function value($k){
        if(!isset($_SESSION[$k]))
            $this->close("SESSION_NOT_DEFINED".__LINE__);
        return $_SESSION[$k];
    }
    public function __get($key)
    {
        echo "tried to call $key";
        return get_instance()->$key;
    }
}

Answer 1

__get method is for accessing undeclared properties of a class.

For calling undeclared functions is __call or __callStatic.

public function __call($method_name, $arguments)
{
    echo "tried to call: $method_name";
}

If you want to use __get - you must call for undefined property. In this case it is not

SessionManager::close()  // call method `close()`

It must be:

$sm = new SessionManager;
$sm->propertyName;   // trying to access undefined property `propertyName` of an object

Take into consideration that

Property overloading only works in object context.

which means that trying to access static property like

SessionManager::staticProperty;

will not work with __get.