[DOC-BUGS] Doc #81386 [Com]: ReflectionProperty::getDefaultValue() and promoted properties

Edit report at https://bugs.php.net/bug.php?id=81386&edit=1

 ID:                 81386
 Comment by:         rafr at generaxion dot dk
 Reported by:        enumag at gmail dot com
 Summary:            ReflectionProperty::getDefaultValue() and promoted
                     properties
 Status:             Open
 Type:               Documentation Problem
 Package:            Documentation problem
 PHP Version:        8.0.9
 Block user comment: N
 Private report:     N

 New Comment:

Honestly I can't find clear documentation outside of this bug report, which stumped me in fixing a queue issue where someone had updated a class constructor

If we could get a promoted property's default value (assuming it has one within the construct), it would as simple as 

$reflection = new \ReflectionClass($this);
$props = $reflection->getProperties();
foreach($props as $prop) {
    if (!$prop->isInitialized($this) && $prop->hasDefaultValue()) {
        $prop->setValue($this, $prop->getDefaultValue());
    }
}

But as is, another loop is needed on top of the previous to ensure all defaults are initialized

foreach($reflection->getConstructor()->getParameters() as $param) {
    if (!$param->isPromoted() || !$param->isOptional()) {
        continue;
    }

    $property = $reflection->getProperty($param->getName());

    if ($property->isInitialized($this)) {
        continue;
    }

    if ($param->isDefaultValueAvailable()) {
        $property->setValue($this, $param->getDefaultValue());
    }
}


Previous Comments:
------------------------------------------------------------------------
[2023-06-08 09:35:54] evgeeek at gmail dot com

Hello!
You can get default values from promoted properties in another way:

readonly class A
{
    public function __construct(
        string $foo,
        private int $bar = 5,
    ) {
    }
}

$ro = new ReflectionClass(A::class);
foreach ($ro->getConstructor()->getParameters() as $param) {
    var_export($param->name);
    var_export($param->isPromoted());
    var_export($param->getType()->getName());
    var_export($param->isDefaultValueAvailable());

    if ($param->isDefaultValueAvailable()) {
        var_export($param->getDefaultValue());
    }
}
//'foo', false, 'string', false
//'bar', true, 'int', true, 5

------------------------------------------------------------------------
[2023-05-02 18:33:09] kevinhawks14 at aol dot com

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------------------------------------------------------------------------
[2022-12-29 15:02:25] hugo dot nicolas dot hn at gmail dot com

Hello, I also stumbled across this "issue" today, and I am in no place to say if this is supposed to be a bug or not, but I wanted to add my experience, being that in addition, if a property is promoted but not typed, its associated ReflectionProperty::hasDefaultValue() seems to always return true.

Test script:
-------------

<?php

class Foo {
    public function __construct(
        public $foo,
        public $bar = 'bar'
        ) {
        }
}

$reflection = new ReflectionClass(Foo::class);
$fooReflection = $reflection->getProperty('foo');
$barReflection = $reflection->getProperty('bar');
var_dump($fooReflection->hasDefaultValue()); // true
var_dump($fooReflection->getDefaultValue()); // null
var_dump($barReflection->hasDefaultValue()); // true
var_dump($barReflection->getDefaultValue()); // null

------------------------------------------------------------------------
[2021-08-26 10:45:54] enumag at gmail dot com

@nikic I have to disagree. As a programmer who is using promoted properties I don't differentiate if the default value is for the property or the parameter. Even if the behavior is expected from the language's point of view, it's not entirely expected from the user's point of view. I'd much rather see it mentioned there than only randomly stumbling on it while debugging.

------------------------------------------------------------------------
[2021-08-26 10:35:40] [email protected]

Promoted properties intentionally don't have a default value. The property is always initialized by the constructor.

I don't think this needs to be mentioned in the ReflectionProperty::getDefaultValue() docs, as reflection simply reflects reality. However, it should be mentioned in the promoted property docs at https://www.php.net/manual/en/language.oop5.decon.php#language.oop5.decon.constructor.promotion.

------------------------------------------------------------------------


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