PHP: rfc:autovivification_false

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
====== PHP RFC: Deprecate autovivification on false ======
  * Date: 2021-05-25
  * Author: Kamil Tekiela <dharman@php.net>
  * Status: Implemented in PHP 8.1
  * Implementation: https://github.com/php/php-src/pull/7131

===== Introduction =====

PHP natively allows for [[https://en.wikipedia.org/wiki/Autovivification|autovivification]] (auto-creation of arrays from falsey values). This feature is very useful and used in a lot of PHP projects, especially if the variable is undefined. However, there is a little oddity that allows creating an array from a false and null value. 

<PHP>
// From undefined
$arr[] = 'some value';
$arr['doesNotExist'][] = 2;
// From false
$arr = false;
$arr[] = 2;
// From null
$arr = null;
$arr[] = 2;
</PHP>

This RFC talks **only about autovivification from %%false%%**. 

===== Proposal =====

The proposal is to disallow autovivification from %%false%% values. We will continue to allow autovivification from undefined variable and %%null%%, but in every other case an error message will be shown:

> Cannot use a scalar value as an array

In PHP 8.1, appending to a variable of type false will display a deprecation notice. For example:

> Deprecated: Automatic conversion of false to array is deprecated in

In PHP 9.0, this will throw a fatal error, the same as for other scalar types. 

===== Rationale =====

Historically, many functions return false on error or array on success. In some scenarios, developers might want to assign an additional element to an array, e.g. a total section at the end of array fetched from PDO. PHP does not complain if the value is %%false%%. Whether it should be considered a bug or a "feature" is up for debate. 

<PHP>
$stmt = $pdo->query("SELECT 1 WHERE 0");
$arr = $stmt->fetch();
// naively try to append
$arr[] = ['new row values'];
</PHP>

Throwing an error in such cases could save developers from common bugs in their code. On the other hand, this feature could also be considered useful by some developers. The rationale here is that the behaviour is inconsistent. Neither true, 0, nor "" can be used in autovivification today, so does it make sense to allow false?

Allowing autovivification on %%null%% can be a sign of a buggy code, but it is less of a problem than %%false%%. In PHP, %%null%% and undefined are very similar and often treated the same way, e.g. %%isset()%% and %%??%%.

===== Backward Incompatible Changes =====

Every single usage autovivification on false will throw a deprecation error in PHP 8.1 and throw a fatal error in PHP 9.0.

===== Vote =====

Should we deprecate autovivification from false?

Started: 2021-06-09T20:00:00Z\\
Ends: 2021-06-23T20:00:00Z

<doodle title="Deprecate autovivification from false?" auth="dharman" voteType="single" closed="true"> 
   * Yes
   * No
</doodle>

===== Discussion on internals ======

https://externals.io/message/114595
Page Tools
