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Date: Sun, 3 Aug 2025 12:17:46 +0200
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Subject: Re: [PHP-DEV] Protected inheritance hierarchies
To: Rob Landers <rob@bottled.codes>
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From: jnv@jnvsor.net (Jonathan Vollebregt)

On 8/3/25 11:30 AM, Rob Landers wrote:
> I'm not sure that this is a bug. You can redeclare the same type and add 
> hooks (or change them), which breaks all assumptions about substitutability.

No it doesn't, read the "Property type variance" section on the property 
hooks RFC:

> Normal properties are neither covariant nor contravariant; their type may not change in a subclass. The reason for that is “get” operations MUST be covariant, and “set” operations MUST be contravariant. The only way for a property to satisfy both requirements is to be invariant.
> 
> With abstract properties (on an interface or abstract class) or virtual properties, it is possible to declare a property that has only a get or set operation. As a result, abstract properties or virtual properties that have only a get operation required MAY be covariant. Similarly, an abstract property or virtual property that has only a set operation required MAY be contravariant.
> 
> Once a property has both a get and set operation, however, it is no longer covariant or contravariant for further extension. That is, it is now invariant (as all properties are in 8.3 and earlier).

Your example code _does_ fail but this isn't because of the hooks (The 
getter from A->$v is inherited in C) it's because you've redeclared it 
without a default value and it's trying to access an uninitialized 
property: https://3v4l.org/pv39f#v8.4.11 vs https://3v4l.org/VD6ZK#v8.4.11