Manual unset and GC

Hello, folks. If this is not the correct place to ask, I apologize. > TL;DR: Does setting a variable to null (or even > unseting it) have **any** effect if that's the last instruction > of a function? The full version of the question with context: I have a question about the inner workings of PHP that was raised by some people at work. In the code we write at the company I work for, there's a guideline to always assign null to the variables of type PdoStatement. Something like the following: ``` $stm = null; ``` I understand this removes the reference to the object, calls the destructor and frees the memory, but the point is: the guideline mandates that we do that even if it is the last instruction of a function, for example: ``` function example(): void { // run your SQL queries $stm = null; } ``` I understand that this last line is not needed and removing it would have literally no effect on the code execution since $stm will go out of scope and the same things (remove reference, call destructor and free memory) will happen exactly the same. While discussing this with a few colleagues it was pointed out that **maybe** PHP will execute the GC immediately when we do $stm = null but not when the variable goes out of scope, making the explicit null as some sort of optimization. I didn't find any resources on the documentation that could point to which assumption is correct, so I post the question here: Does setting a variable to null (or even unseting it) have **any** effect if that's the last instruction of a function? Thank you