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Date: Thu, 20 Nov 2025 16:19:09 +0300
Message-ID: <CAPyeZ4PvBx6Q22dDGBXxufNu8-SjKLGxiTMPFSLb9COMgbVjAA@mail.gmail.com>
Subject: [PHP-DEV] First-class constructor callables
To: php internals <internals@lists.php.net>
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From: udaltsov.valentin@gmail.com (Valentin Udaltsov)

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Hello internals,

I'd like to explore the possibility of adding a first-class callable syntax
for object constructors:

```
$factory = new Foo(...);
```

The idea is that this expression would produce a Closure which, when
invoked, calls the constructor with the provided arguments:

```
$factory = new Foo(...);
$object = $factory($arg1, $arg2);
```

This would conceptually mirror the existing first-class callable notation
for functions and methods: trim(...), $object->method(...),
Foo::method(...).

Today, the equivalent form requires boilerplate such as:

```
$factory = static fn($arg): Foo => new Foo($arg);
```

or defining a static factory:

```
class Foo
{
    public static function new($arg): self
    {
        return new self($arg);
    }
}

$factory = Foo::new(...);
```

However, the latter is not possible for 3rd-party classes.

Question for Larry and Arnaud:

In PFA v2
<https://wiki.php.net/rfc/partial_function_application_v2#constructors>,
you note that constructor references pose significant technical challenges.
Could you elaborate on what those challenges are and whether they are
fundamental, or potentially addressable with a more limited or explicit
syntax such as `new Foo(...)`?

You also mention that "the use cases for partially applying a constructor
are few, especially now that we have lazy objects (as of PHP 8.4)." I tend
to disagree. For cases like:

```
$numbers = array_map(new BcMath\Number(...), $numericStrings);
```

lazy objects do not help, and a constructor-as-callable form remains
valuable.

Best regards,
Valentin

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<div dir=3D"ltr"><div>Hello internals,<br><br>I&#39;d like to explore the p=
ossibility of adding a first-class callable syntax for object constructors:=
<br><br>```<br>$factory =3D new Foo(...);<br>```<br><br>The idea is that th=
is expression would produce a Closure which, when invoked, calls the constr=
uctor with the provided arguments:<br><br>```<br>$factory =3D new Foo(...);=
<br>$object =3D $factory($arg1, $arg2);<br>```<br><br>This would conceptual=
ly mirror the existing first-class callable notation for functions and meth=
ods: trim(...), $object-&gt;method(...), Foo::method(...).<br><br>Today, th=
e equivalent form requires boilerplate such as:<br><br>```<br>$factory =3D =
static fn($arg): Foo =3D&gt; new Foo($arg);<br>```<br><br>or defining a sta=
tic factory:<br><br>```<br>class Foo<br>{<br>=C2=A0 =C2=A0 public static fu=
nction new($arg): self<br>=C2=A0 =C2=A0 {<br>=C2=A0 =C2=A0 =C2=A0 =C2=A0 re=
turn new self($arg);<br>=C2=A0 =C2=A0 }<br>}<br><br>$factory =3D Foo::new(.=
..);<br>```<br><br>However, the latter is not possible for 3rd-party classe=
s.<br><br>Question for Larry and Arnaud:<br><br>In <a href=3D"https://wiki.=
php.net/rfc/partial_function_application_v2#constructors">PFA v2</a>, you n=
ote that constructor references pose significant technical challenges.<br>C=
ould you elaborate on what those challenges are and whether they are fundam=
ental, or potentially addressable with a more limited or explicit syntax su=
ch as `new Foo(...)`?<br><br>You also mention that &quot;the use cases for =
partially applying a constructor are few, especially now that we have lazy =
objects (as of PHP 8.4).&quot; I tend to disagree. For cases like:<br><br>`=
``<br>$numbers =3D array_map(new BcMath\Number(...), $numericStrings);<br>`=
``<br><br>lazy objects do not help, and a constructor-as-callable form rema=
ins valuable.<br><br>Best regards,<br>Valentin</div></div>

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