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Date: Fri, 17 May 2024 21:47:41 +0000
To: "php internals" <internals@lists.php.net>
Subject: Re: [PHP-DEV] [DISCUSSION] Checking uninitialized class properties
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From: larry@garfieldtech.com ("Larry Garfield")

On Fri, May 17, 2024, at 9:40 PM, Luigi Cardamone wrote:
> Hello Internals,
> during last PHPDay in Verona I discussed this topic with some of
> you and it was suggested to me to send an email here.
>
> Here is an example to describe my problem. Imagine a simple
> DTO like this:
>
> class MyDTO{
>     public ?int $propA;
>     public ?int $propB;
> }
>
> Imagine that a Form processor or a generic mapper fill some of
> these fields with a null value:
>
> $dto = new MyDTO();
> $dto->propA = null;
>
> Sometimes we use DTOs to handle PATCH requests and not all
> the properties are mapped with a value. In a scenario like this,
> "null" is often a valid value.
>
> At this point, I need a way to find if a property was initialized or
> not but unfortunately "isset" is not a solution. When I write:
>
> echo isset($dto->propA) ? 'init' : 'not-init';
>
> I get "not-init" since isset returns true only if the variable is set
> and different from null.
>
> Full example: https://3v4l.org/4cCj0
>
> Is the language missing a clean way to check if a property is
> initialized or not? Is there any solution to this problem?
>
> The only alternative is using reflection but I need to pass the
> property name as a string losing static analysis.
> Proposing a new language syntax like
> "is_initialized($dto->propA)" can be an interesting solution?
>
> Thank you in advance.

This is a gap in the current API, and I've run into it myself.  What I figured out was:

array_key_exists($prop, get_object_vars($obj))

Because get_object_vars() omits uninitialized values.

I would absolutely like a better alternative.

--Larry Garfield