Serialization of 'Closure' is not allowed

[cambridgeandy]

Hi,

I'm using an object to manage my initialization.

I'm looking at the documentation at ​https://developer.wordpress.org/reference/functions/register_activation_hook/

When I register a hook using a closure (callable) that invokes a method on the object I get an error saying that "Serialization of 'Closure' is not allowed thrown at line [599] in file var/www/html/wp-includes/functions.php"

Here is my offending code:

register_activation_hook(WPMP_BASE_FILE_NAME, function() use ($initialize_service) {
    $initialize_service->activate();
});`

Looking at the code in functions.php I can see that there are checks if the data is an array or an object:

if ( is_array( $data ) || is_object( $data ) ) {
    return serialize( $data );
	

The issue is that the Closure is seen as an object, but cannot be serialized (see ​https://3v4l.org/s23qj)

A potential fix could be:

function maybe_serialize( $data ) {
	if ( is_array( $data ) || is_object( $data ) ) {
		try {
			return serialize( $data );
		} catch (\Throwable $e) {
			return $data;
		}

	}

However, this requires PHP7.0 which would violate the requirement for WP core to support 5.6

[praem90]

PHP can't serialize closure directly. We can use ​https://github.com/opis/closure package for this support.

So, it recommended to use something like below may help to fix your problem.

<?php
register_activation_hook(WPMP_BASE_FILE_NAME, array($initialize_service, 'activate'))