Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:123342
Precedence: bulk
MIME-Version: 1.0
References: <CAAX=eQNH0xyoRkMDThvG_aNS5Hub3tFD52v4PY3OZKT_zWaMmg@mail.gmail.com>
In-Reply-To: <CAAX=eQNH0xyoRkMDThvG_aNS5Hub3tFD52v4PY3OZKT_zWaMmg@mail.gmail.com>
Date: Sat, 18 May 2024 11:19:34 +0200
Message-ID: <CAPzBOBN1M3H-ueqUtzfb_HPv2jZeDaYVTvXideVnx9QYG6LKeA@mail.gmail.com>
Subject: Re: [PHP-DEV] [DISCUSSION] Checking uninitialized class properties
To: Luigi Cardamone <cardamoneluigi@gmail.com>
Cc: internals@lists.php.net
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
From: landers.robert@gmail.com (Robert Landers)

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 val=
ue:

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