PHP RFC: Your Title Here

• Version: 0.1
• Date: 2023-04-15
• Author: Rowan Tommins (imsop@php.net)
• Thanks: Nicolas Grekas (nicolasgrekas@php.net), Ilija Tovilo (tovilo.ilija@gmail.com)
• Status: Draft
• First Published at: http://wiki.php.net/rfc/property-capture

Anonymous classes were introduced in PHP 7.0, using a syntax that allows declaring a class definition and constructing an instance in a single statement. However, unlike anonymous functions, it is not easy to “capture” values from the parent scope for use inside the class; they can only be passed in via an explicit constructor or other method.

This RFC proposes a “property capture” syntax, where a property can be declared and initialised with $instance = new class use($captured) {}; Optional access modifiers, type, and renaming are also supported, e.g. $instance = new class use($localName as private readonly int $propertyName) {};

A new “use clause” is introduced, immediately after the keywords “new class”, with the syntax use (<var-name> as <modifiers> <type> <property-name>, ...). The <modifiers>, <type>, and <property-name> are all optional; if none is specified, the “as” keyword must be omitted.

The simplest form of property capture resembles the capture list of anonymous functions:

$foo = 1;
$bar = 2;
$anon = new class use ($foo, $bar) {};

This declares a class with public untyped properties $foo and $bar, and creates an instance populating them from the outer variables $foo and $bar. In other words, it is equivalent to this:

$foo = 1;
$bar = 2;
$anon = new class($foo, $bar) {
    var $foo;
    var $bar;
 
    public function __construct($foo, $bar) {
        $this->foo = $foo;
        $this->bar = $bar;
    }
};

By default, the property takes the same name as the outer variable, but this can be over-ridden using the syntax $varName as $propName. This also allows the same local variable to be captured as the initial value for more than one property. For example:

$foo = 1;
$bar = 2;
$anon = new class use ($foo as $one, $bar as $two, $bar as $three) {};

Is equivalent to:

$foo = 1;
$bar = 2;
$anon = new class($foo, $bar, $bar) {
    var $one;
    var $two;
    vat $three;
 
    public function __construct($one, $two, $three) {
        $this->one = $one;
        $this->two = $two;
        $this->three = $three;
    }
};

The as keyword can also be used to modify the visibility and/or type of the declared property, either instead of or as well as renaming the property.

The modifiers allowed are the same as for Constructor Property Promotion, which is used internally to declare the properties; that is currently:

• One of public, protected, or private
• Optional readonly, which must be combined with a type specification
• A type specification

For example:

$foo = 1;
$bar = 2;
$anon = new class use ($foo as private, $bar as protected readonly int, $bar as ?int $alsoBar) {};

Is equivalent to:

$foo = 1;
$bar = 2;
$anon = new class($foo, $ba, $bar) {
    private $foo;
    protected readonly int $bar;
    var ?int $alsoBar;
 
    public function __construct($foo, $bar, $alsoBar) {
        $this->foo = $foo;
        $this->bar = $bar;
        $this->alsoBar = $alsoBar;
    }
};

What breaks, and what is the justification for it?

Next PHP 8.x (hopefully 8.3)

Describe the impact to CLI, Development web server, embedded PHP etc.

Will existing extensions be affected?

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