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Date: Wed, 11 Jun 2025 10:30:47 +0200
Message-ID: <CANS-=pfn1_o3pha9ymiBpNGX9b5k56=pmMf=Pk3igyThqn6XfA@mail.gmail.com>
Subject: Re: [PHP-DEV] Feature Discussion |
To: Dmitry Derepko <xepozzd@gmail.com>
Cc: PHP internals <internals@lists.php.net>
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From: kjarli@gmail.com (Lynn)

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On Mon, Jun 9, 2025 at 7:36=E2=80=AFPM Dmitry Derepko <xepozzd@gmail.com> w=
rote:

> Hello, Internals!
>
> I've implemented an alpha implementation of the Extension Functions in PH=
P.
> Basically, it's a syntax sugar of the imperative call of the function wit=
h
> the passing the object as a first argument, but anyway.
>
> Here is how it looks like in Kotlin:
> https://kotlinlang.org/docs/extensions.html
>
> In PHP it might looks like so:
>
> function stdClass.getName() {
>     return $this->name;
> }
>
> $obj =3D new stdClass;
> $obj->name =3D 'Dmitrii';
> echo $obj->getName(); // prints Dmitrii
>
> so desugared version is:
>
> function getName(stdClass $obj) {
>     return $obj->name;
> }
>
> $obj =3D new stdClass;
> $obj->name =3D 'Dmitrii';
> echo getName($obj); // prints Dmitrii
>
> Quite simple improvement, but a really convenient way to "attach"
> behaviour and extend vendor code to make it more readable.
>
> Functions register as usual, using `use` keyword. So there are no
> surprises when you call a function which does not exist, only an implicit
> way to specify the function.
>
> "Attaching" the function with the name of an existing member
> function raises an exception.
> But you may juggle different functions from different namespaces:
>
> namespace A;
>
> use function aa; // from global namespace
> OR
> use function B\aa; // from B namespace
> OR
> use function B\aa as Baa; // from B namespace with alias
>
> `use function` construction may be enlarged with the "extension" keyword:
> use function getTime; // regular function
> use extension function getTime; // extension function, unable to call
> without correct receiver
>
> As in Kotlin, it should access only public members.
>
> class A { private $name; }
>
> function A.getName() {
>     return $this->name; // raises an exception because private and
> protected members aren't available
> }
>
> Supporting types DNF is under question, but I'd leave them as future scop=
e.
>
> function ((A&B)|null).smth() { ... }
> but it could be resolved to
> function smth((A&B)|null $obj) { ... }
>
> The dot as a delimiter is also under the question, here are a few options=
:
>
> function stdClass::getName();
> function stdClass->getName();
> function stdClass.getName();
> function ::stdClass getName();
> function stdClass<-getName();
> function getName of stdClass();
>
> etc.
>
> I've tried to implement the feature through attaching a function to the
> class functions scope, which is wrong and does not follow the requirement=
s.
> It has memory leaks.
>
> https://github.com/php/php-src/compare/master...xepozz:php-src:extension-=
functions?expand=3D1#diff-1dd36b02e5025ec3a5a546f8e41374ee4fc18c411bce447dd=
1dc2952329ccbe6R25
>
> I also thought about adding this feature as a custom attribute behaviour,
> but it's a way difficult:
>
> #[Extension("stdClass")]
> function hasName(): bool {
>     return $this->name;
> }
>
> I can try to implement the de-sugared version to make it work correctly.
>
> ---
>
> WDYT guys?
>
> --
> Best regards,
> Dmitrii Derepko.
> @xepozz
>

It's an interesting concept, and reminds me of how Lua handles this with
`string.len(theVariable)` vs `theVariable:len()`. The way you define the
function with a dot or colon, determines whether or not you have `self`
(`$this`) available or not. Feature wise, what would be use-cases to have
this?

DTOs in libraries, but perhaps also value objects could add a custom
factory function. I don't want my database models/entities to know about
the DTO, but the (vendor) DTO can't know about the database model/entity
either. This scenario would be to define a runtime static function to
create the object, and perhaps even a runtime function the other way around
to populate my entity based on the DTO. I could keep this code separate
from both classes and merely have it act as a glue. I don't know if this is
a good practice though.

What about interfaces and abstract classes, would these functions fulfill
contracts in any way? It sounds like runtime traits in that regard, but
makes static code analysis a lot more complex; not only for tools, but also
for humans to parse and understand. Would runtime traits be an alternate
solution to function extension to deal with autoloading?

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<div dir=3D"ltr"><div dir=3D"ltr"><div dir=3D"ltr"><br></div><br><div class=
=3D"gmail_quote gmail_quote_container"><div dir=3D"ltr" class=3D"gmail_attr=
">On Mon, Jun 9, 2025 at 7:36=E2=80=AFPM Dmitry Derepko &lt;<a href=3D"mail=
to:xepozzd@gmail.com">xepozzd@gmail.com</a>&gt; wrote:<br></div><blockquote=
 class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px so=
lid rgb(204,204,204);padding-left:1ex"><div dir=3D"ltr"><div>Hello, Interna=
ls!</div><div><br></div><div>I&#39;ve implemented an alpha implementation o=
f the Extension Functions in PHP.</div><div>Basically, it&#39;s a syntax su=
gar of the imperative call of the function with the passing the object as a=
 first argument, but anyway.</div><div><br></div><div>Here is how it looks =
like in Kotlin:=C2=A0<a href=3D"https://kotlinlang.org/docs/extensions.html=
" target=3D"_blank">https://kotlinlang.org/docs/extensions.html</a></div><d=
iv><br></div><div>In PHP it might looks like so:</div><div><br></div><div>f=
unction stdClass.getName() {=C2=A0</div><div>=C2=A0 =C2=A0 return $this-&gt=
;name;</div><div>}</div><div><br></div><div>$obj =3D new stdClass;</div><di=
v>$obj-&gt;name =3D &#39;Dmitrii&#39;;</div><div>echo $obj-&gt;getName(); /=
/ prints Dmitrii</div><div><br></div><div>so desugared version is:</div><di=
v><br></div><div><div>function getName(stdClass $obj) {=C2=A0</div><div>=C2=
=A0 =C2=A0 return $obj-&gt;name;</div><div>}</div><div><br></div><div>$obj =
=3D new stdClass;</div><div>$obj-&gt;name =3D &#39;Dmitrii&#39;;</div><div>=
echo getName($obj); // prints Dmitrii</div><div><br></div></div><div>Quite =
simple improvement, but a really convenient way to &quot;attach&quot; behav=
iour and extend vendor=C2=A0code to make it more readable.</div><div><br></=
div><div>Functions register as usual, using `use` keyword. So there are no =
surprises=C2=A0when you call a function which does not exist, only an impli=
cit way to specify the function.</div><div><br></div><div>&quot;Attaching&q=
uot; the function with the name of an existing member function=C2=A0raises =
an exception.</div><div>But you may juggle different functions from differe=
nt namespaces:</div><div><br></div><div>namespace A;</div><div><br></div><d=
iv>use function aa; // from global namespace</div><div>OR</div><div>use fun=
ction B\aa; // from B namespace</div><div>OR</div><div>use function B\aa as=
 Baa; // from B namespace with alias</div><div><br></div><div>`use function=
` construction may be enlarged with the &quot;extension&quot; keyword:</div=
><div>use function getTime; // regular function</div><div>use extension fun=
ction getTime; // extension function, unable to call without correct receiv=
er</div><div><br></div><div>As in Kotlin, it should access only public memb=
ers.</div><div><br></div><div>class A { private $name; }</div><div><br></di=
v><div>function A.getName() {=C2=A0</div><div>=C2=A0 =C2=A0 return $this-&g=
t;name; // raises an exception because private and protected members aren&#=
39;t available</div><div>}</div><div><br></div><div>Supporting types DNF is=
 under question, but I&#39;d leave them as future scope.</div><div><br></di=
v><div><div>function ((A&amp;B)|null).smth() { ... }</div><div>but it could=
 be resolved to</div><div>function smth((A&amp;B)|null $obj) { ... }</div><=
div><br></div></div><div>The dot as a delimiter is also under the question,=
 here are a few options:</div><div><br></div><div>function stdClass::getNam=
e();</div><div>function stdClass-&gt;getName();</div><div>function stdClass=
.getName();</div><div>function ::stdClass getName();</div><div>function std=
Class&lt;-getName();</div><div>function getName of stdClass();</div><div><b=
r></div><div>etc.</div><div><br></div><div>I&#39;ve tried to implement the =
feature through attaching a function to the class functions scope, which is=
 wrong and does not follow the requirements. It has memory leaks.</div><div=
><a href=3D"https://github.com/php/php-src/compare/master...xepozz:php-src:=
extension-functions?expand=3D1#diff-1dd36b02e5025ec3a5a546f8e41374ee4fc18c4=
11bce447dd1dc2952329ccbe6R25" target=3D"_blank">https://github.com/php/php-=
src/compare/master...xepozz:php-src:extension-functions?expand=3D1#diff-1dd=
36b02e5025ec3a5a546f8e41374ee4fc18c411bce447dd1dc2952329ccbe6R25</a></div><=
div><br></div><div>I also thought about adding this feature as a custom att=
ribute behaviour, but it&#39;s a way difficult:</div><div><br></div><div>#[=
Extension(&quot;stdClass&quot;)]<br>function hasName(): bool {<br>=C2=A0 =
=C2=A0 return $this-&gt;name;<br>}</div><div><br></div><div>I can try to im=
plement the de-sugared version to make it work correctly.</div><div><br></d=
iv><div>---</div><div><div><br>WDYT guys?</div><div><br></div></div><span c=
lass=3D"gmail_signature_prefix">-- </span><br><div dir=3D"ltr" class=3D"gma=
il_signature"><div dir=3D"ltr"><div style=3D"color:rgb(34,34,34)">Best rega=
rds,</div><div style=3D"color:rgb(34,34,34)"><div dir=3D"ltr"><div dir=3D"l=
tr">Dmitrii Derepko.</div><div><a>@xepozz</a></div></div></div></div></div>=
</div></blockquote><div><br></div><div>It&#39;s an interesting concept, and=
 reminds me of how Lua handles this with `string.len(theVariable)` vs `theV=
ariable:len()`. The way you define the function with a dot or colon, determ=
ines whether or not you have `self` (`$this`) available or not. Feature wis=
e, what would be use-cases to have this?</div><div><br></div><div>DTOs in l=
ibraries, but perhaps also value objects could add a custom factory functio=
n. I don&#39;t want my database models/entities to know about the DTO, but =
the (vendor) DTO can&#39;t know about the database model/entity either. Thi=
s scenario would be to define a runtime static function to create the objec=
t, and perhaps even a runtime function the other way around to populate my =
entity based on the DTO. I could keep this code separate from both classes =
and merely have it act as a glue. I don&#39;t know if this is a good practi=
ce though.</div><div><br></div><div>What about interfaces and abstract clas=
ses, would these functions fulfill contracts in any way? It sounds like run=
time traits in that regard, but makes static code analysis a lot more compl=
ex; not only for tools, but also for humans to parse and understand. Would =
runtime traits be an alternate solution to function extension to deal with =
autoloading?</div><div><br></div></div></div></div>

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