Forem: Neloy Ahmed

The story of readonly classes and properties in php

Neloy Ahmed — Tue, 20 Dec 2022 04:14:08 +0000

PHP 8.2 introduced the new feature of readonly classes. Before learning about readonly classes let's have a flashback and discuss readonly properties so that we can grasp the idea properly.

Readonly properties:

PHP 8.1 introduced the feature of readonly property. The concept of readonly property in PHP is as simple as when a class property is declared using the readonly modifier you will not be able to modify the property after initialization.

<?php

class User 
{
   public readonly string $name;

   public function __construct(string $name) {
       // Legal initialization.
       $this->name = $name;
   }
}

$john = new User("John");
// Legal read.
var_dump($john->name); // string(4) "John"

// Illegal reassignment. It does not matter that the assigned value is the same.
$john->name = "John";
// Error: Cannot modify readonly property User::$name
?>

There are some important notes to remember about readonly properties in PHP.

You can only apply readonly modifier on typed properties . A readonly property without type constraints can be created using the Mixed type.
You can not assign readonly modifier on static properties.

class User 
{
 static readonly string $name;
// Fatal error: Static property User::$name cannot be readonly
}

You can initialize the readonly property once, and only from the scope where it has been declared. Any other assignment or modification of the property will result in an Error exception.

<?php
class User 
{
  public readonly string $name;
}

$john = new User;
// Illegal initialization outside of private scope.
$john->name = "John";
// Error: Cannot initialize readonly property User::$name from global scope
?>

You can not assign default value on readonly properties, because a readonly property with a default value is essentially the same as a constant, and thus not particularly useful.

<?php

class User {
    // Fatal error: Readonly property User::$age cannot have default value
    public readonly int $age = 22;
}
?>

You can not unset() readonly properties once they are initialized. However, it is possible to unset a readonly property prior to initialization, from the scope where the property has been declared.
Not only plain assignments, any type of modification of readonly property will also result in an Error exception:

<?php

class User {
  public function __construct(
  public readonly int $age = 22,
  public readonly array $ary = [],
  ) {}
}

$john = new User;

// Cannot modify readonly property User::$age
$john->age += 1;

// Cannot modify readonly property User::$age
$john->age++;

// Cannot modify readonly property User::$age
++$john->age;

// Cannot modify readonly property User::$ary
$john->ary[] = 1;

// Cannot modify readonly property User::$ary
$john->ary[0][] = 1;

// Cannot modify readonly property User::$age
$ref =& $john->age;

// Cannot modify readonly property User::$age
$john->age =& $ref;

// Cannot acquire reference to readonly property User::$age
foreach ($john as &$prop);
?>

However, objects (or resources) stored in readonly properties may still be modified internally:

<?php

class User {
  public function __construct(public readonly object $userProfile) {}
}

$john = new User(new stdClass);

// Legal interior mutation.
$john->userProfile->gender = "Male";

// Illegal reassignment.
$john->userProfile = new stdClass;

?>

Readonly classes:

Now as we got the concept of readonly property it will be very easier for us to understand readonly classes in PHP.

If we define a class as readonly all the declared property of that class will automatically become readonly property.

readonly class User
{
    public string $name;
    public string $gender;
}

So, User::$name and User::$gender are now readonly properties. To achieve this previously in PHP 8.1 we had to do something like:

class User
{
    public readonly string $name;
    public readonly string $gender;
}

From this observation, we can say that readonly classes are syntactic sugar that will make all the declared properties of that class readonly properties.

So, we have to remember that, all those important notes that we described about readonly properties are still applicable here. Such as:

A readonly class can not contain untyped or static properties.
A readonly class's property cannot have a default value. etc.
Another important note to remember about readonly classes is that A readonly class can only be extended if, the child class is also a readonly class.

That's all for today, thank you for reading.

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How to run USSD code in Linux

Neloy Ahmed — Fri, 15 Oct 2021 16:51:02 +0000

Recently in one of my home PC I removed windows and installed Ubuntu 20.04.3 LTS.

One of the very first challenges I faced was making sure I can connect to the internet using my D-Link DWM-157 modem.
I was able to connect to the internet using my modem pretty easily. Now it's time to face the next one - I was not able to find a way to check my SIM balance or internet balance by running USSD code (e.g. *123# etc).

After doing some google search I came to know about ‘Modem Manager GUI’ and I was so happy. Opened my terminal and simply typed:
sudo apt-get update sudo apt-get install modem-manager-gui

Someone was smiling behind the scene and was whispering not so easy boy! Prepare for the next hurdle.

I was so happy it is a very nice GUI, everything is here for me i just a single click away to check anything. Everything was working perfectly in the GUI except the USSD code !
When i submit USSD code it refuses me with following error:

Modem Manager >= 0.7.0: GDBus.Error:org.freedesktop.ModemManager1.Error.Core.Aborted: USSD terminated by network

I did not find any work around to solve this issue.

Then I came to know about a command line application called "gammu".
sudo apt-get install gammu

After installing gammu created the configuration file for gammu using the command: gammu-detect > .gammurc

This command created a hidden configuration file in the home folder. ctrl+h to view hidden files.

Opened the configuration file created and checked for the devices detected by gammu. There were devices listed as ttyUSB0, ttyUSB1, ttyUSB2 etc. ttyUSB0 to ttyUSB3 belongs to the D-Link modem.

Disconnected from the internet to send ussd code (because it was required).

Now to send a ussd, type the following command in the terminal: gammu getussd "USSD_CODE". For example gammu getussd *125#

But each time I ran that command after waiting for some time I was refused by this error message:

No response in specified timeout. Probably the phone is not connected.

Although my modem was connected properly.

I also tried with adding the device number along with the above command ie, gammu 1 getussd *125# or gammu 2 getussd *125# etc.

But i was continuously getting follow messages:

Warning: No configuration file found!
Error: Failed to read [gammu1] section from configuration file (gammurc)!
Warning: No configuration read, using builtin defaults!
No response in specified timeout. Probably the phone is not connected.

End of another frustrating tryout!

Then i came to know that i can send ussd code using picocom by giving AT commands. To install picocom: sudo apt install picocom

Now again to issue the AT commands i have to disable internet connection to free the modem.

Next i need to find out the various ports of the modem using: ls /dev/ttyU*

Usually 3 ports will be returned :

dialogue port (i.e. 1st port) is /dev/ttyUSB0
audio port (i.e. 2nd port) is /dev/ttyUSB1 (audio and microphone if supported)
sms & internet aka data port (i.e. 3rd port) is /dev/ttyUSB3

I started picocom on the dialogue port:
sudo picocom -c /dev/ttyUSB0
the -c means local echo on, making AT commands visible as i type.

Now check USSD:
AT+CUSD=1,"*333#"

But success is yet one step away!!! I was not able to type properly in the terminal. So i changed port and and started picocom on other ports available from : ls /dev/ttyU*

sudo picocom -c /dev/ttyUSB1

And finally the success! Yesssssssss…
Now i am able to run any ussd code using following format :
AT+CUSD=1,"*333#"

To quit picocom, first press CTRL+a followed by a regular x

Thank you.