to support php 5.6 and 7.1 you can't do either of those, since runkit doesn't work on php 7, and uopz 5 doesn't work on php 5

I don't see anything in the php documentation that would indicate a requirement to use global variables here. "use" declares that $id is inherited from parent scope, which is the scope the function was defined in, and that's definitely the case here.

This probably depends on the current working dir from which the main script runs. Better to incorporate __DIR__ here.

if $this->id is never read, why do you need to write to it?

Ship It!