PHP RFC: Warnings for PHP 8.5

• Version: 0.1
• Date: 2025-07-14
• Author: Gina Peter Banyard girgias@php.net
• Status: Under Discussion
• Target Version: PHP 8.5
• Implementation: TBD
• First Published at: https://wiki.php.net/rfc/warnings-php-8-5

The RFC proposes to add a few warnings when encountering certain edge cases in PHP 8.5, and promote those to error in PHP 9.

The following list provides a short overview of the warnings being introduced, while more detailed explanation is provided in the Proposal section:

• Coercing NAN to other types
• Destructuring non-array values
• Using offsets on non-container values in isset()/empty()
• Using invalid offset types when checking string offsets with isset()/empty()

Each proposed warning is voted separately and requires a 2/3 majority.

• Author: Gina Peter Banyard girgias@php.net

The floating point value NAN is returned by functions to indicate some sort of error.

However, NAN can be coerced to other types without error and hide bugs (except for functions requiring an int). More concerning is that the value NAN is considered truthy and will be coerced to the value true, except when using an explicit (int) cast, in which case it is coerced to 0 which is falsy.

As having a NAN value is unlikely and points to some sort of bug in the code, we propose to emit the following warning when NAN is coerced (be that implicitly or explicitly) to another type:

Warning: unexpected NAN value was coerced to TYPE

This affects passing NAN as an argument to parameters which do not declare float as a type, all casting operators, logical operators, if statements, and ternary operator.

• Author: Gina Peter Banyard girgias@php.net

The list($v1, $v2) = $array or [$v1, $v2] = $array language construction allows destructing array values into their own variables.

When attempting to destructure an object, the following Error is thrown:

Error: Cannot use object of type stdClass as array

However, when using scalar values (bool, int, float, string), null, or resource no Error is thrown, and each variable is assigned null.

We propose to emit the following warning when destructuring non-array values:

Warning: Cannot use TYPE as array

• Author: Gina Peter Banyard girgias@php.net

This is lifted from the Improve language coherence for the behaviour of offsets and containers RFC as it is time-sensitive.

When attempting to check if an offset exists or is empty on objects that do not implement ArrayOffset (or the relevant C object handlers) then the following error is thrown:

Error: Cannot use object of type TYPE as array

However, when using scalar values (bool, int, float, string), null, or resource no Error is thrown and false is returned for isset() and true is returned for empty().

As this points to some code expectation being violated, we propose to emit the following warning when using a scalar value or a resource as a container:

Warning: Cannot use TYPE as array

We do not propose to warn when using null as a container, as null supports auto-vivification to array, and can be used as a sentinel value.

• Author: Gina Peter Banyard girgias@php.net

This is lifted from the Improve language coherence for the behaviour of offsets and containers RFC as it is time-sensitive.

When attempting to check an array offset with isset() or empty(), with an object or array as the offset, the following TypeError is thrown:

TypeError: Illegal offset type in isset or empty

This is similar to a TypeError being thrown by the ArrayAccess::offsetExists() (/the equivalent C object handler) for some internal classes like SplFixedArray.

However, when using a string as a container (e.g. $string[$offset]) invalid offsets are ignored and false is returned for isset() and true is returned for empty(). This behaviour is even stranger, as the null-coalescing operator does throw the following TypeError, using the following code snippet as an example:

$s = 'abcdefg';
$o = new stdClass();
var_dump(isset($s[$o]));
var_dump($s[$o] ?? 'z');

we get the following:

bool(false)
Fatal error: Uncaught TypeError: Cannot access offset of type stdClass on string

As this likely points to a bug, and to normalize the behaviour with the null coalesced operator, we propose to emit the following warning when using an invalid offset type for a string offset:

Warning: Cannot access offset of type TYPE on string

For PHP 8.5 additional warnings will be emitted. The promotions of warnings to the appropriate Error will happen no earlier than PHP 9.