Execute purely anonymous function in PHP

Question

What's the suggested way to execute an anonymous function in PHP similar to how Javascript provides this possibility?

Javascript:

(function(){ console.log('Hello!'); })();

Trying the same in PHP yields a syntax error for the parameters opening bracket. I've found a way around this problem by "mis-using" call_user_func():

PHP:

call_user_func(function(){ echo "Hello!"; });

But the PHP documentation (update: the German version of the docs) explicitly says the first parameter to call_user_func() should be a string... So I'm not sure if my solution is supposed to work correct (however, it does for the moment).

The purpose behind this solution - similar to the reason why you would do it the same way in JavaScript - is to not pollute the global namespace for some added functionality. This script is auto-prepended for all scripts on the whole server and should be hidden wrt global namespace and global scope. It's not meant to be invisible - just keep symbols out of the namespace.

Answer 1

But the PHP documentation explicitly says the first parameter to call_user_func() should be a string

No it doesn't.

mixed call_user_func ( callable $callback [, mixed $parameter [, mixed $... ]] )

The first parameter is of type callable, so your code is perfectly valid :)

Answer 2

Your solution is appropriate. The first argument to call_user_func should be a callable, a type which includes closures.