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References: <3A6.1T4AB.9eXWvq4hof.1cHcqE@seznam.cz>
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Date: Thu, 16 May 2024 17:11:50 -0700
Message-ID: <CAMrTa2F7Yt7N5bbegtrFCakew6EAOtm49Ohs5+_2H1O1Gy98JA@mail.gmail.com>
Subject: Re: [PHP-DEV] [RFC] [Vote] Type Guards for Classes
To: =?UTF-8?Q?Patrik_V=C3=A1clavek?= <PaTrOnY@email.cz>
Cc: internals@lists.php.net
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From: jordan.ledoux@gmail.com (Jordan LeDoux)

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On Thu, May 16, 2024 at 1:32=E2=80=AFPM Patrik V=C3=A1clavek <PaTrOnY@email=
.cz> wrote:

> Introduction
> *************
>
> This RFC proposes a new feature in PHP: type guards for classes (or
> interfaces). This feature aims to simplify and standardize the process of
> verifying that a variable is an instance of a specific class, enhancing
> code readability and reducing boilerplate code.
>
> Motivation
> *************
>
> Currently, in PHP, to ensure that a variable is an instance of a specific
> class, developers need to use the `instanceof` operator and manually thro=
w
> an exception if the check fails. This results in repetitive boilerplate
> code scattered throughout the codebase. A new syntax, `(ClassName)
> $variable`, is proposed to streamline this process by performing an
> instanceof check and throwing a `TypeError` if the variable is not an
> instance of the specified class.
>
> Proposal
> ***********
>
> Introduce a new type guard syntax for classes:
>
> ```php
> (Foo) $variable;
> ```
>
> This syntax will internally perform the following operations:
>
> 1. Check if `$variable` is an instance of `Foo`.
> 2. If the check fails, throw a `TypeError` with a message indicating the
> expected and actual types.
>
> Example:
> Consider the following class definition:
>
> ```php
> class Foo {
>    // class definition
> }
> ```
>
> To ensure a variable is an instance of `Foo`, instead of writing:
>
> ```php
> if (!$variable instanceof Foo) {
>     throw new TypeError('Expected instance of Foo, got ' .
> gettype($variable));
> }
> ```
>
> Developers can use the new type guard syntax:
>
> ```php
> (Foo) $variable;
> ```
>
> Backward Compatibility
> ***************************
>
> This feature introduces new syntax and does not affect existing code. It
> is fully backward-compatible, as it does not modify or deprecate any
> existing functionality.
>

Since this throws, I'm struggling to understand how this would replace any
usages of `instanceof` other than `if (!($var instanceof Foo)) throw new
TypeError();`

Also, this is not an RFC with a page I can look at OR something in a vote,
so the subject line is a bit of a lie.

But now that I've gotten my grumps out of the way, better class specific
syntax is in general something that I think is positive and worth exploring=
.

Jordan

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<div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=3D"gmail_quote">=
<div dir=3D"ltr" class=3D"gmail_attr">On Thu, May 16, 2024 at 1:32=E2=80=AF=
PM Patrik V=C3=A1clavek &lt;<a href=3D"mailto:PaTrOnY@email.cz">PaTrOnY@ema=
il.cz</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"ma=
rgin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:=
1ex"><div><div>Introduction</div><div>*************</div><div><br></div><di=
v>This RFC proposes a new feature in PHP: type guards for classes (or inter=
faces). This feature aims to simplify and standardize the process of verify=
ing that a variable is an instance of a specific class, enhancing code read=
ability and reducing boilerplate code.</div><div><br></div><div>Motivation<=
/div><div>*************<br></div><div><br></div><div>Currently, in PHP, to =
ensure that a variable is an instance of a specific class, developers need =
to use the `instanceof` operator and manually throw an exception if the che=
ck fails. This results in repetitive boilerplate code scattered throughout =
the codebase. A new syntax, `(ClassName) $variable`, is proposed to streaml=
ine this process by performing an instanceof check and throwing a `TypeErro=
r` if the variable is not an instance of the specified class.</div><div><br=
></div><div>Proposal</div><div>***********<br></div><div><br></div><div>Int=
roduce a new type guard syntax for classes:</div><div><br></div><div>```php=
</div><div>(Foo) $variable;</div><div>```</div><div><br></div><div>This syn=
tax will internally perform the following operations:</div><div><br></div><=
div>1. Check if `$variable` is an instance of `Foo`.</div><div>2. If the ch=
eck fails, throw a `TypeError` with a message indicating the expected and a=
ctual types.</div><div><br></div><div>Example:</div><div>Consider the follo=
wing class definition:</div><div><br></div><div>```php</div><div>class Foo =
{</div><div>=C2=A0 =C2=A0// class definition</div><div>}</div><div>```</div=
><div><br></div><div>To ensure a variable is an instance of `Foo`, instead =
of writing:</div><div><br></div><div>```php</div><div>if (!$variable instan=
ceof Foo) {</div><div>=C2=A0 =C2=A0 throw new TypeError(&#39;Expected insta=
nce of Foo, got &#39; . gettype($variable));</div><div>}</div><div>```</div=
><div><br></div><div>Developers can use the new type guard syntax:</div><di=
v><br></div><div>```php</div><div>(Foo) $variable;</div><div>```</div><div>=
<br></div><div>Backward Compatibility</div><div>***************************=
<br></div><div><br></div><div>This feature introduces new syntax and does n=
ot affect existing code. It is fully backward-compatible, as it does not mo=
dify or deprecate any existing functionality.</div></div></blockquote><div>=
<br></div><div>Since this throws, I&#39;m struggling to understand how this=
 would replace any usages of `instanceof` other than `if (!($var instanceof=
 Foo)) throw new TypeError();`</div><div><br></div><div>Also, this is not a=
n RFC with a page I can look at OR something in a vote, so the subject line=
 is a bit of a lie.</div><div><br></div><div>But now that I&#39;ve gotten m=
y grumps out of the way, better class specific syntax is in general somethi=
ng that I think is positive and worth exploring.</div><div><br></div><div>J=
ordan <br></div></div></div>

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