Why Does My PHP Code Throw a 'Fatal error: Constant Expression Contains Invalid Operations' Error When Initializing a Static Variable?

PHP Fatal Error: Constant Expression Invalid Operations

When encountering the error "Fatal error: Constant expression contains invalid operations," it arises when a PHP static variable attempts to initialize with a non-literal or non-constant value before PHP 5.6.

In your case, the line in question:

protected static $dbname = 'mydb_'.$appdata['id'];

attempts to initialize the static property $dbname with the value of the dynamic variable $appdata['id']. However, static properties require initialization with constants or literals before PHP 5.6.

The reason behind this is that static declarations are evaluated at compile-time, which means the PHP interpreter cannot access dynamic variables that are only known at runtime. To resolve this error, you could:

• Replace $appdata['id'] with a constant string: Ensure that the database name is a fixed value and assign it directly, e.g., protected static $dbname = 'mydb_my_app';.
• Remove the static attribute: If it's not necessary for $dbname to be static, declare it as a regular variable without the static keyword, e.g., protected $dbname = 'mydb_my_app';.

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