Serialization of Closure Not Allowed

Why This Happens

PHP's built-in serialization does not support closures (anonymous functions). This error occurs when you try to serialize an object that contains a closure, store it in a session, or cache it. Closures capture scope and cannot be reliably converted to a string representation.

The Problem

$callback = function ($x) { return $x * 2; };
$_SESSION['callback'] = $callback; // Cannot serialize closure

The Fix

// Option 1: Use a named function or class
class Doubler {
    public function __invoke(int $x): int {
        return $x * 2;
    }
}
$_SESSION['callback_class'] = Doubler::class;

// Option 2: Store the operation name
$_SESSION['operation'] = 'double';
$operations = [
    'double' => fn($x) => $x * 2,
];

Step-by-Step Fix

1. 1

   Find the closure

   Identify which variable contains a closure that is being serialized. Check objects stored in sessions or caches.

2. 2

   Extract to a class

   Convert the closure to an invokable class that implements the same logic and can be serialized.

3. 3

   Store references instead

   Instead of serializing the closure, store an identifier or class name and recreate the callable when needed.