I am getting an error:
Fatal error: Constant expression contains invalid operations in config.php on line 214
That line was:
protected static $dbname = 'mydb_'.$appdata['id']; Whether I did any mistakes in quotes? Or somewhere else?
My search for the error message only showed a different source cause (a dynamic default value in a function definition).
From the official Php documentation :
Like any other PHP static variable, static properties may only be initialized using a literal or constant before PHP 5.6; expressions are not allowed. In PHP 5.6 and later, the same rules apply as const expressions: some limited expressions are possible, provided they can be evaluated at compile time.
So you cannot initialize a static variable with another variable. Replace $appdata['id'] with a constant string or remove the static attribute.
This is because all static declarations are resolved in compile-time, when the content of other variables is not known (see this other page of official doc).
Unless you mess with reflection, the only way I can think of to have a static private/protected class property with a dynamically generated value is to calculate it outside the class:
class Foo { protected static string $dbname = DBNAME; public static function debug(): string { return Foo::$dbname; } } $appdata = [ 'id' => 31416, ]; define('DBNAME', 'mydb_' . $appdata['id']); var_dump(Foo::debug()); In your precise use case, however, it's possible that there's simply no good reason for the property to be static. In that case, it's as straightforward as using the constructor:
class Foo { protected string $dbname; public function __construct(array $appdata) { $this->dbname = 'mydb_' . $appdata['id']; } public function debug(): string { return $this->dbname; } } $appdata = [ 'id' => 31416, ]; $foo = new Foo($appdata); var_dump($foo->debug()); 
This is because a static variable contains a constant value in it. But in your case:
protected static $dbname = 'mydb_'.$appdata['id']; $appdata['id'] is dynamic that can change its value during the execution. That's why the error is showing.
I had this error and my fix was to not declare a date within a class property array
public static $config_array = array( 'start_date' => date('Y-m-d H:i:s') // No can do ); In my case the solution to this issue was to create a singleton class so the variable's value is initialized (calculated) only once and still have access to it whenever I need.
(Extra info: The singleton is a design pattern which stricts you to have only 0 or 1 instance of your class in your entire program. There are several design pattern, I collected 115 of them so far on a single image)
In your case the code would look like this:
class DataBaseConfig { private static $instance; private $dbname ; private final function __construct() { $this->dbname = 'mydb_'.$appdata['id']; } public static function getName() { if (!isset(self::$instance)) { self::$instance = new DataBaseConfig(); } return self::$instance->dbname; } } You can use it like DataBaseConfig::getName() for the shortest / simplest version.
In reality you have more complex classes and functions so by defining a getInstance() function you will avoid repeating the <check instance> - <create instance process> lines for every function you add.
(Extra info: 2 synonym paradigms DRY - Don't Repeat Yourself and DIE - Duplication Is Evil)
This is the refactoring you need:
public static function getInstance() { if (!isset(self::$instance)) { self::$instance = new PhpStarter(); } return self::$instance; } public function getName() { return $this->dbname; } Use it like $db = DataBaseConfig::getInstance(); then $db->getName() and $db->getSomethingElse() for the other functions.
For your information:- I got the same error by using some characters in a constant expressions.
public static $dbPassword="mAkE-34@-||sR"; This is what caused the error and I removed this || which is the logical OR operator characters from the string and it worked.