Backward Incompatible Changes

PHP Core

$GLOBALS Access Restrictions

Access to the $GLOBALS array is now subject to a number of restrictions. Read and write access to individual array elements like $GLOBALS['var'] continues to work as-is. Read-only access to the entire $GLOBALS array also continues to be supported. However, write access to the entire $GLOBALS array is no longer supported. For example, array_pop($GLOBALS) will result in an error.

Usage of static Variables in Inherited Methods

When a method using static variables is inherited (but not overridden), the inherited method will now share static variables with the parent method.

class A {
public static function
counter() {
$counter = 0;
B extends A {}
var_dump(A::counter()); // int(1)
var_dump(A::counter()); // int(2)
var_dump(B::counter()); // int(3), previously int(1)
var_dump(B::counter()); // int(4), previously int(2)
This means that static variables in methods now behave the same way as static properties.

Optional parameters specified before required parameters

An optional parameter specified before required parameters is now always treated as required, even when called using named arguments. As of PHP 8.0.0, but prior to PHP 8.1.0, the below emits a deprecation notice on the definition, but runs successfully when called. As of PHP 8.1.0, an error of class ArgumentCountError is thrown, as it would be when called with positional arguments.

function makeyogurt($container = "bowl", $flavour)
"Making a $container of $flavour yogurt.\n";
makeyogurt(flavour: "raspberry");
catch (
Error $e)
get_class($e), ' - ', $e->getMessage(), "\n";

Output of the above example in PHP 8.0:

Deprecated: Required parameter $flavour follows optional parameter $container
 in example.php on line 3
Making a bowl of raspberry yogurt.

Output of the above example in PHP 8.1:

Deprecated: Optional parameter $container declared before required parameter
 $flavour is implicitly treated as a required parameter in example.php on line 3
ArgumentCountError - makeyogurt(): Argument #1 ($container) not passed

Note that a default value of null can be used before required parameters to specify a nullable type, but the parameter will still be required.

Return Type Compatibility with Internal Classes

Most non-final internal methods now require overriding methods to declare a compatible return type, otherwise a deprecated notice is emitted during inheritance validation. In case the return type cannot be declared for an overriding method due to PHP cross-version compatibility concerns, a ReturnTypeWillChange attribute can be added to silence the deprecation notice.

New Keywords

readonly is a keyword now. However, it still may be used as function name.

never is now a reserved word, so it cannot be used to name a class, interface or trait, and is also prohibited from being used in namespaces.

Resource to Object Migration

Several resources have been migrated to objects. Return value checks using is_resource() should be replaced with checks for false.


mysqli_fetch_fields(), and mysqli_fetch_field_direct() will now always return 0 for the max_length. This information can be computed by iterating over the result set, and taking the maximum length. This is what PHP was doing internally previously.

The MYSQLI_STMT_ATTR_UPDATE_MAX_LENGTH option no longer has any effect.

The MYSQLI_STORE_RESULT_COPY_DATA option no longer has any effect. Passing any value to the mode parameter of mysqli::store_result() no longer has any effect.

mysqli::connect() now returns true instead of null on success.

The default error handling mode has been changed from "silent" to "exceptions" See the MySQLi reporting mode page for more details on what this entails, and how to explicitly set this attribute. To restore the previous behaviour use: mysqli_report(MYSQLI_REPORT_OFF);

Classes extending mysqli_stmt::execute() are now required to specify the additional optional parameter.


The mysqlnd.fetch_data_copy INI directive has been removed. This should not result in user-visible behavior changes.


EC private keys will now be exported in PKCS#8 format rather than traditional format, just like all other keys.

openssl_pkcs7_encrypt() and openssl_cms_encrypt() will now to default using AES-128-CBC rather than RC2-40. The RC2-40 cipher is considered insecure and not enabled by default by OpenSSL 3.

PHP Data Objects

PDO::ATTR_STRINGIFY_FETCHES now stringifies values of type bool to "0" or "1". Previously bools were not stringified.

Calling PDOStatement::bindColumn() with PDO::PARAM_LOB will now constantly bind a stream result when PDO::ATTR_STRINGIFY_FETCHES is not enabled. Previously, the result would either be a stream or a string depending on the used database driver and the time the binding is performed.

MySQL Driver

Integers and floats in result sets will now be returned using native PHP types instead of strings when using emulated prepared statements. This matches the behavior of native prepared statements. The previous behaviour can be restored by enabling the PDO::ATTR_STRINGIFY_FETCHES option.

SQLite Driver

Integers and floats in results sets will now be returned using native PHP types. The previous behaviour can be restored by enabling the PDO::ATTR_STRINGIFY_FETCHES option.


To comply with the ArrayAccess interface, Phar::offsetUnset() and PharData::offsetUnset() no longer return a bool.


version_compare() no longer accepts undocumented operator abbreviations.

htmlspecialchars(), htmlentities(), htmlspecialchars_decode(), html_entity_decode(), and get_html_translation_table() now use ENT_QUOTES | ENT_SUBSTITUTE rather than ENT_COMPAT by default. This means that ' is escaped to &#039; while previously nothing was done. Additionally, malformed UTF-8 will be replaced by a Unicode substitution character, instead of resulting in an empty string.

debug_zval_dump() now prints the refcount of a reference wrappers with their refcount, instead of only prepending & to the value. This more accurately models reference representation since PHP 7.0.

debug_zval_dump() now prints interned instead of a dummy refcount for interned strings and immutable arrays.

Standard PHP Library (SPL)

SplFixedArray, will now be JSON encoded like an array

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