property-of<...> Utility type

[supun-io]

Problem: an easy way to access the names of the properties of an object or a class.

Solution: property-of<MyObject> utility type

Example:

class CreateSubscriberDto
{

    public string $email;
    public int $listId;

    /**
     * @param property-of<self> $property
     * @return bool
     */
    public function hasProperty(string $property): bool
    {
        dumpType($property); // 'email'|'listId'

        // ...
    }

}

$dto = new CreateSubscriberDto();
$dto->hasProperty('email'); // no error
$dto->hasProperty('listId'); // no error
$dto->hasProperty('notExisting'); // shows static error

TODO:

• Implement a template-supported version in PHPStan\Type\Generic

Notes:

Most of the code was taken from KeyOfType.

If the idea is accepted, I will work on the implementation of the template-supported version.

[herndlm]

jfyi this is also related to what I was asking recently in phpstan/phpstan#12240. consider this a neutral comment, I don't mean that adding it here is good or bad.

this is a highly specific thing potentially, but having a utility for this in phpstan itself might make sense. in my case I needed something even more special for our app in the end anyway, because I also had to check if the property has a default value assigned or not. so I ended up with a properties-without-default-value-of<> utility to make some risky behaviour we have more (type-)safe 😊

[ondrejmirtes]

I've rejected this in the past because different users might have different needs. There are many decisions about object properties you need to make:

• Only native properties, or with magic properties (@method, __get etc.) as well?
• Only public properties, or private+protected as well?
• Only instance properties, or static properties too?
• What about universalObjectCratesClasses? Does this return a general array<string, mixed> for them or not?

Because of these uncertainties, every project can implement their own version using https://phpstan.org/developing-extensions/custom-phpdoc-types.

[supun-io]

yes, I understand that there are variations of the problem, but still, this is a very common case in PHP, especially when using DTOs.

Would it make sense to have a second parameter that accepts a ReflectionProperty constant to cover all the cases including static virtual, set, final, etc.

// all
property-of<self>

// static only
property-of<self, ReflectionProperty::IS_STATIC>

// protected or private
property-of<self, ReflectionProperty::IS_PROTECTED | ReflectionProperty::IS_PRIVATE>

// static and public
property-of<self, ReflectionProperty::IS_STATIC & ReflectionProperty::IS_PUBLIC>

We can simply pass the second parameter to getProperties of the class reflection. This is assuming PHPDoc can parse bitwise operators correctly (which I am not sure)

This solution solves:

• Only native properties,
• Only public properties, or private+protected as well?
• Only instance properties, or static properties too?

But not

• magic properties (@method, __get etc.) as well?
  I think we could somehow support @method, but __get is going to be difficult

• What about universalObjectCratesClasses? Does this return a general array<string, mixed> for them or not?
  Just mixed for them?