PHP Error : Fatal error: Constant expression contains invalid operations
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());
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).
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.