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Date: Mon, 10 Mar 2025 17:37:28 +0000
To: internals@lists.php.net, Vinicius Dias <carlosv775@gmail.com>,
 PHP internals <internals@lists.php.net>
Subject: Re: [PHP-DEV] Manual unset and GC
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From: derick@php.net (Derick Rethans)

On 10 March 2025 16:15:16 GMT, Vinicius Dias <carlosv775@gmail=2Ecom> wrote=
:
>Hello, folks=2E If this is not the correct place to ask, I apologize=2E
>
>> TL;DR: Does setting a variable to `null` (or even `unset`ing 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=2E
>
>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`=2E
>Something like the following:
>
>```
>$stm =3D 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
>
> $stm =3D null;
>}
>```
>
>I understand that this last line is not needed and removing it would
>have literally no effect on the code execution since `$stm` will go
>out of scope and the same things (remove reference, call destructor
>and free memory) will happen exactly the same=2E
>
>While discussing this with a few colleagues it was pointed out that
>**maybe** PHP will execute the GC immediately when we do `$stm =3D null`
>but not when the variable goes out of scope, making the explicit null
>as some sort of optimization=2E
>
>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 `unset`ing it) have **any**
>effect if that's the last instruction of a function?
>
>Thank you

No=2E

It has no effect=2E At the end of the function PHP would remove a ref to t=
he variable anyway=2E Setting it to null first is an action that will take =
time, unless opcache is turned on and realises it's a useless action=2E

cheers
Derick