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Date: Sat, 18 May 2024 14:34:16 +0200
Message-ID: <CAPzBOBMNRz=ZGKOspHa2hGhxCBU9mbfN9kiH0ZDEyd__j3S4cg@mail.gmail.com>
Subject: Re: [PHP-DEV] [DISCUSSION] Checking uninitialized class properties
To: Luigi Cardamone <cardamoneluigi@gmail.com>
Cc: internals@lists.php.net
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From: landers.robert@gmail.com (Robert Landers)

On Sat, May 18, 2024 at 12:52=E2=80=AFPM Luigi Cardamone
<cardamoneluigi@gmail.com> wrote:
>
> Thank you for your feedback.
>
> I am already using a solution like the one
> proposed by Robert: it works but it
> leaves some doubts since each project
> can have a different name for NotSet
> while it seems a general concept of the
> language.
>
> Besides the example I proposed, I think
> that there are many cases where you
> can check if the property is initialised
> or not and for consistency "null" should
> be considered a valid initialization value.
>
> Are there any downsides in adding a
> specific syntax to check if a property
> is initialized with any value?
>
> Thank you.
>
> Luigi Cardamone
> Backend developer
> Italy
>
> Il Sab 18 Mag 2024, 11:19 Robert Landers <landers.robert@gmail.com> ha sc=
ritto:
>>
>> On Fri, May 17, 2024 at 11:43=E2=80=AFPM Luigi Cardamone
>> <cardamoneluigi@gmail.com> 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 =3D new MyDTO();
>> > $dto->propA =3D null;
>> >
>> > Sometimes we use DTOs to handle PATCH requests and not all
>> > the properties are mapped with a value. In a scenario like this,
>> > "null" is often a valid value.
>> >
>> > At this point, I need a way to find if a property was initialized or
>> > not but unfortunately "isset" is not a solution. When I write:
>> >
>> > echo isset($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.
>> >
>> > Luigi Cardamone
>> > Backend developer
>> > Italy
>>
>> I wouldn't rely on checking initialized or not. Instead, use a sentinel =
value:
>>
>> class NotSet {}
>>
>> define("NotSet", new NotSet());
>>
>> class MyAwesomeValue {
>>     public NotSet|null|string $aValue =3D NotSet;
>> }
>>
>> This way, even programmers can "unset" a property by simply setting
>> $value->aValue =3D NotSet without having to rely on the weird PHP
>> semantics of unsetting a property. You can also use this to
>> declaratively encode which properties cannot be unset, without having
>> to define it in your mapping code.
>>
>> Robert Landers
>> Software Engineer
>> Utrecht NL

Please remember to bottom post!

> it works but it
> leaves some doubts since each project
> can have a different name for NotSet
> while it seems a general concept of the
> language.

Why does it need to be consistent between projects? Most languages
simply set uninitialized values as `null`, and every project across
all languages will have to solve this differently, specific to their
project.

For PHP projects, it really depends on how you want to handle it in
your project. I have a project where an uninitialized value during
serialization/deserialization is an error because that means someone
forgot to map something or the end-user forgot a field in their
request. In another project, values are uninitialized on purpose and
accessing properties goes through __set and  __get.

I don't think there's a silver bullet here.

> I think
> that there are many cases where you
> can check if the property is initialised
> or not and for consistency "null" should
> be considered a valid initialization value.

Well, that depends on your application's business logic and model. A
bank account probably shouldn't be allowed to have a null balance, a
player have a null position, or a farmer have null goats.

> Are there any downsides in adding a
> specific syntax to check if a property
> is initialized with any value?

Personally, I've used such a check so rarely and when I've done so, it
has been in the context of reflection, for which there is a method on
ReflectionProperty
(https://www.php.net/manual/en/reflectionproperty.isinitialized.php)
to check for it. I've never needed to know the difference between
uninitialized and null during regular runtime and $value ?? $default
has always been what I've needed.

In your case, this would probably be all you need:

https://3v4l.org/p1nAHJ

I guess this is a pretty good use case for nameof which keeps staying
down near the bottom of todo list lately...

Robert Landers
Software Engineer
Utrecht NL