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Date: Wed, 6 Apr 2022 13:03:57 +0100
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Subject: [RFC] Undefined Property Error Promotion
From: marandall@php.net (Mark Randall)
Message-ID: <php.internals-117481@news.php.net>

Internals,

Part 2 of the undefined behaviour improvements, this time focusing on 
properties.

https://wiki.php.net/rfc/undefined_property_error_promotion

This RFC draws heavily from the just passed undefined variables error 
promotion RFC, and is intended to compliment both it, and the 8.2 
Deprecate Dynamic Properties RFC.

The arguments in favour are the same as the last one, reading things 
which don't exist will often lead to the program entering an unintended 
state, and is likely the result of a programming error.

There is a difference though that we do explicitly provide an object 
that is designed to be dynamic, and that is stdClass which is the 
typical output from json_decode and array to object casts.

I would expect we might want to discuss special-casing the accessing of 
properties on stdClass and leave them as a warning.

However, I personally think that for the sake of consistency we should 
make undefined properties throw across the board, including stdClass.

We already have fully backwards compatible mechanisms built into the 
language (isset, empty, null coalesce, property_exists) to safely handle 
cases of the property not being defined, even on objects that do not 
have a fixed structure.

I was originally going to include a section for discussion about 
potentially using AllowDynamicProperties to pull double duty, allowing 
reads without an error as well, but I do not believe that would be in 
the best interests of the language, and so removed it.

Mark Randall