Property hooks with defaults

[SerafimArts]

Description

@iluuu1994 hell again! I brought a little more on the properties, again)

Possibly related with #15419

https://3v4l.org/EbvOM/rfc#vgit.master

The following code:

<?php

final class Example1
{
    public string $name = 'asd' {
        set(string $value) {
            $this->name = $value;
        }
    }
}

final class Example2
{
    public string $name = 'asd' {
        set(string $value) {
            throw new \Exception('Cannot update value');
            $this->name; // lel)
        }
    }
}

final class Example3
{
    public string $name = 'asd' {
        set(string $value) {
            // $this->name = $value;
        }
    }
}


final class Example4
{
    public string $name = 'asd' {
        set(string $value) {
            throw new \Exception('Cannot update value');
        }
    }
}

Resulted in this output:

Example1: OK
Example2: OK
Example3: Cannot specify default value for virtual hooked property Example3::$name
Example4: Cannot specify default value for virtual hooked property Example4::$name

Example3 and Example4 throws an exeption

But I expected this output instead:

Example1: OK
Example2: OK
Example3: OK
Example4: OK

PHP Version

PHP 8.4.1 (+ current master)

Operating System

No response

[iluuu1994]

Virtual properties cannot set default values. Can you explain why you think this is a bug?

https://wiki.php.net/rfc/property-hooks#default_values

Default values are supported on properties that have a backing store. Default values are not supported on virtual properties, as there is no natural value for the default to be assigned to, and will be treated as a compile-time error.

[SerafimArts]

Virtual properties cannot set default values. Can you explain why you think this is a bug?

What about Example2 vs Example4?

P.S. Example number 2 is working, but the RFC says that it should not work.

Perhaps then the expected result should be like this?

Example1: OK
Example2: Cannot specify default value for virtual hooked property Example2::$name 
Example3: Cannot specify default value for virtual hooked property Example3::$name
Example4: Cannot specify default value for virtual hooked property Example4::$name

[SerafimArts]

Hmmm... I don't quite understand what a "backing store" is. Could you please clarify?

[iluuu1994]

@SerafimArts A backing value is some storage a hooked property can use to store a value. It is added automatically depending on whether the hook uses the $this->property syntax. When it is not used, the storage is removed to 1. reduce memory and 2. remove it from outputs like var_dump(), serialize(), etc. Such properties are called virtual, the opposite are called backed properties. Check the Detailed Proposal section, it's explained there.