Re: Declaration-aware attributes

On Tue, May 30, 2023 at 2:49 AM Andreas Hennings <andreas@dqxtech.net> wrote: > Hello internals, > I am picking up an idea that was mentioned by Benjamin Eberlei in the past. > https://externals.io/message/110217#110395 > (we probably had the idea independently, but Benjamin's is the first > post where I see it mentioned in the list) > > Quite often I found myself writing attribute classes that need to fill > some default values or do some validation based on the symbol the > attribute is attached to. > E.g. a parameter attribute might require a specific type on that > parameter, or it might fill a default value based on the parameter > name. > > Currently I see two ways to do this: > 1. Do the logic in the code that reads the attribute, instead of the > attribute class. This works ok for one-off attribute classes, but it > becomes quite unflexible with attribute interfaces, where 3rd parties > can provide their own attribute class implementations. > 2. Add additional methods to the attribute class that take the symbol > reflector as a parameter, like "setReflectionMethod()", or > "setReflectionClass()". Or the method in the attribute class that > returns the values can have a reflector as a parameter. > > Both of these are somewhat limited and unpleasant. > > I want to propose a new way to do this. > Get some feedback first, then maybe an RFC. > > The idea is to mark constructor parameters of the attribute class with > a special parameter attribute, to receive the reflector. > The other arguments are then shifted to skip the "special" parameter. > > #[Attribute] > class A { > public function __construct( > public readonly string $x, > #[AttributeContextClass] > public readonly \ReflectionClass $class, > public readonly string $y, > ) {} > } > > $a = (new ReflectionClass(C::class))->getAttributes()[0]->newInstance(); > assert($a instanceof A); > assert($a->x === 'x'); > assert($a->class->getName() === 'C'); > assert($a->y === 'y'); > > Note that for methods, we typically need to know the method reflector > _and_ the class reflector, because the method could be defined in a > base class. > > #[Attribute] > class AA { > public function __construct( > #[AttributeContextClass] > public readonly \ReflectionClass $class, > #[AttributeContextMethod] > public readonly ReflectionMethod $method, > ) {} > } > > class B { > #[AA] > public function f(): void {} > } > > class CC extends B {} > > $aa = (new ReflectionMethod(CC::class, > 'f))->getAttributes()[0]->newInstance(); > assert($a->class->getName() === 'CC'); > assert($a->method->getName() === 'f'); > > --- > > Notice that the original proposal by Benjamin would use an interface > and a setter method, ReflectorAwareAttribute::setReflector(). > > I prefer to use constructor parameters, because I generally prefer if > a constructor creates a complete and immutable object. > Thank you bringing this up, the more I work with attributes the more often this comes up. I think when we designed the attributes there was just so little concrete exprimentation that we didn't pick this up as a serious missing gap. As for implementation, reviewing the whole e-mail thread, i like both: 1, ReflectionAttribute::getReflectionTarget() - this we should add no matter what and is a no brainer 2. An argument attribute that instructs newInstance() to inject the reflector or the ReflectionAttribute, for example #[AttributeContext] or #[AttributeTargetReflector] > > ---- > > Thoughts? > > -- Andreas > > -- > PHP Internals - PHP Runtime Development Mailing List > To unsubscribe, visit: https://www.php.net/unsub.php > >