array ( 0 => 'index.php', 1 => 'PHP Manual', ), 'head' => array ( 0 => 'UTF-8', 1 => 'en', ), 'this' => array ( 0 => 'migration80.incompatible.php', 1 => 'Backward Incompatible Changes', 2 => 'Backward Incompatible Changes', ), 'up' => array ( 0 => 'migration80.php', 1 => 'Migrating from PHP 7.4.x to PHP 8.0.x', ), 'prev' => array ( 0 => 'migration80.new-classes.php', 1 => 'New Classes and Interfaces', ), 'next' => array ( 0 => 'migration80.deprecated.php', 1 => 'Deprecated Features', ), 'alternatives' => array ( ), 'source' => array ( 'lang' => 'en', 'path' => 'appendices/migration80/incompatible.xml', ), 'history' => array ( ), ); $setup["toc"] = $TOC; $setup["toc_deprecated"] = $TOC_DEPRECATED; $setup["parents"] = $PARENTS; manual_setup($setup); contributors($setup); ?>

Backward Incompatible Changes

PHP Core

String to Number Comparison

Non-strict comparisons between numbers and non-numeric strings now work by casting the number to string and comparing the strings. Comparisons between numbers and numeric strings continue to work as before. Notably, this means that 0 == "not-a-number" is considered false now.
Comparison Before After
0 == "0" true true
0 == "0.0" true true
0 == "foo" true false
0 == "" true false
42 == " 42" true true
42 == "42foo" true false

Other incompatible Changes

  • match is now a reserved keyword.

  • mixed 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.

  • Assertion failures now throw by default. If the old behavior is desired, assert.exception=0 can be set in the INI settings.

  • Methods with the same name as the class are no longer interpreted as constructors. The __construct() method should be used instead.

  • The ability to call non-static methods statically has been removed. Thus is_callable() will fail when checking for a non-static method with a classname (must check with an object instance).

  • The (real) and (unset) casts have been removed.

  • The track_errors ini directive has been removed. This means that php_errormsg is no longer available. The error_get_last() function may be used instead.

  • The ability to define case-insensitive constants has been removed. The third argument to define() may no longer be true.

  • The ability to specify an autoloader using an __autoload() function has been removed. spl_autoload_register() should be used instead.

  • The errcontext argument will no longer be passed to custom error handlers set with set_error_handler().

  • create_function() has been removed. Anonymous functions may be used instead.

  • each() has been removed. foreach or ArrayIterator should be used instead.

  • The ability to unbind this from closures that were created from a method, using Closure::fromCallable() or ReflectionMethod::getClosure(), has been removed.

  • The ability to unbind this from proper closures that contain uses of this has also been removed.

  • The ability to use array_key_exists() with objects has been removed. isset() or property_exists() may be used instead.

  • The behavior of array_key_exists() regarding the type of the key parameter has been made consistent with isset() and normal array access. All key types now use the usual coercions and array/object keys throw a TypeError.

  • Any array that has a number n as its first numeric key will use n+1 for its next implicit key, even if n is negative.

  • The default error_reporting level is now E_ALL. Previously it excluded E_NOTICE and E_DEPRECATED.

  • display_startup_errors is now enabled by default.

  • Using parent inside a class that has no parent will now result in a fatal compile-time error.

  • The @ operator will no longer silence fatal errors (E_ERROR, E_CORE_ERROR, E_COMPILE_ERROR, E_USER_ERROR, E_RECOVERABLE_ERROR, E_PARSE). Error handlers that expect error_reporting to be 0 when @ is used, should be adjusted to use a mask check instead:

    <?php
    // Replace
    function my_error_handler($err_no, $err_msg, $filename, $linenum) {
    if (    error_reporting() == 0) {
    return     false;
    }
    // ...
    }

    // With
    function my_error_handler($err_no, $err_msg, $filename, $linenum) {
    if (!(    error_reporting() & $err_no)) {
    return     false;
    }
    // ...
    }
    ?>

    Additionally, care should be taken that error messages are not displayed in production environments, which can result in information leaks. Please ensure that display_errors=Off is used in conjunction with error logging.

  • #[ is no longer interpreted as the start of a comment, as this syntax is now used for attributes.

  • Inheritance errors due to incompatible method signatures (LSP violations) will now always generate a fatal error. Previously a warning was generated in some cases.

  • The precedence of the concatenation operator has changed relative to bitshifts and addition as well as subtraction.

    <?php
    echo "Sum: " . $a + $b;
    // was previously interpreted as:
    echo ("Sum: " . $a) + $b;
    // is now interpreted as:
    echo "Sum:" . ($a + $b);
    ?>

  • Arguments with a default value that resolves to null at runtime will no longer implicitly mark the argument type as nullable. Either an explicit nullable type, or an explicit null default value has to be used instead.

    <?php
    // Replace
    function test(int $arg = CONST_RESOLVING_TO_NULL) {}
    // With
    function test(?int $arg = CONST_RESOLVING_TO_NULL) {}
    // Or
    function test(int $arg = null) {}
    ?>

  • A number of warnings have been converted into Error exceptions:

    • Attempting to write to a property of a non-object. Previously this implicitly created an stdClass object for null, false and empty strings.
    • Attempting to append an element to an array for which the PHP_INT_MAX key is already used.
    • Attempting to use an invalid type (array or object) as an array key or string offset.
    • Attempting to write to an array index of a scalar value.
    • Attempting to unpack a non-array/Traversable.
    • Attempting to access unqualified constants which are undefined. Previously, unqualified constant accesses resulted in a warning and were interpreted as strings.
    • Passing the wrong number of arguments to a non-variadic built-in function will throw an ArgumentCountError.
    • Passing invalid countable types to count() will throw a TypeError.

    A number of notices have been converted into warnings:

    • Attempting to read an undefined variable.
    • Attempting to read an undefined property.
    • Attempting to read an undefined array key.
    • Attempting to read a property of a non-object.
    • Attempting to access an array index of a non-array.
    • Attempting to convert an array to string.
    • Attempting to use a resource as an array key.
    • Attempting to use null, a boolean, or a float as a string offset.
    • Attempting to read an out-of-bounds string offset.
    • Attempting to assign an empty string to a string offset.

  • Attempting to assign multiple bytes to a string offset will now emit a warning.

  • Unexpected characters in source files (such as NUL bytes outside of strings) will now result in a ParseError exception instead of a compile warning.

  • Uncaught exceptions now go through "clean shutdown", which means that destructors will be called after an uncaught exception.

  • The compile time fatal error "Only variables can be passed by reference" has been delayed until runtime, and converted into an "Argument cannot be passed by reference" Error exception.

  • Some "Only variables should be passed by reference" notices have been converted to "Argument cannot be passed by reference" exception.

  • The generated name for anonymous classes has changed. It will now include the name of the first parent or interface:

    <?php
    new class extends ParentClass {};
    // -> ParentClass@anonymous
    new class implements FirstInterface, SecondInterface {};
    // -> FirstInterface@anonymous
    new class {};
    // -> class@anonymous
    ?>

    The name shown above is still followed by a NUL byte and a unique suffix.

  • Non-absolute trait method references in trait alias adaptations are now required to be unambiguous:

    <?php
    class X {
    use     T1, T2 {
    func as otherFunc;
    }
    function     func() {}
    }
    ?>

    If both T1::func() and T2::func() exist, this code was previously silently accepted, and func was assumed to refer to T1::func. Now it will generate a fatal error instead, and either T1::func or T2::func needs to be written explicitly.

  • The signature of abstract methods defined in traits is now checked against the implementing class method:

    <?php
    trait MyTrait {
    abstract private function     neededByTrait(): string;
    }

    class     MyClass {
    use     MyTrait;

    // Error, because of return type mismatch.
    private function neededByTrait(): int { return 42; }
    }
    ?>

  • Disabled functions are now treated exactly like non-existent functions. Calling a disabled function will report it as unknown, and redefining a disabled function is now possible.

  • data:// stream wrappers are no longer writable, which matches the documented behavior.

  • The arithmetic and bitwise operators +, -, *, /, **, %, <<, >>, &, |, ^, ~, ++, -- will now consistently throw a TypeError when one of the operands is an array, resource or non-overloaded object. The only exception to this is the array + array merge operation, which remains supported.

  • Float to string casting will now always behave locale-independently.

    <?php
    setlocale    (LC_ALL, "de_DE");
    $f = 3.14;
    echo     $f, "\n";
    // Previously: 3,14
    // Now: 3.14
    ?>

    See printf(), number_format() and NumberFormatter() for ways to customize number formatting.

  • Support for deprecated curly braces for offset access has been removed.

    <?php
    // Instead of:
    $array{0};
    $array{"key"};
    // Write:
    $array[0];
    $array["key"];
    ?>

  • Applying the final modifier on a private method will now produce a warning unless that method is the constructor.

  • If an object constructor exit()s, the object destructor will no longer be called. This matches the behavior when the constructor throws.

  • Namespaced names can no longer contain whitespace: While Foo\Bar will be recognized as a namespaced name, Foo \ Bar will not. Conversely, reserved keywords are now permitted as namespace segments, which may also change the interpretation of code: new\x is now the same as constant('new\x'), not new \x().

  • Nested ternaries now require explicit parentheses.

  • debug_backtrace() and Exception::getTrace() will no longer provide references to arguments. It will not be possible to change function arguments through the backtrace.

  • Numeric string handling has been altered to be more intuitive and less error-prone. Trailing whitespace is now allowed in numeric strings for consistency with how leading whitespace is treated. This mostly affects:

    • The is_numeric() function
    • String-to-string comparisons
    • Type declarations
    • Increment and decrement operations

    The concept of a "leading-numeric string" has been mostly dropped; the cases where this remains exist in order to ease migration. Strings which emitted an E_NOTICE "A non well-formed numeric value encountered" will now emit an E_WARNING "A non-numeric value encountered" and all strings which emitted an E_WARNING "A non-numeric value encountered" will now throw a TypeError. This mostly affects:

    • Arithmetic operations
    • Bitwise operations

    This E_WARNING to TypeError change also affects the E_WARNING "Illegal string offset 'string'" for illegal string offsets. The behavior of explicit casts to int/float from strings has not been changed.

  • Magic Methods will now have their arguments and return types checked if they have them declared. The signatures should match the following list:

    • __call(string $name, array $arguments): mixed
    • __callStatic(string $name, array $arguments): mixed
    • __clone(): void
    • __debugInfo(): ?array
    • __get(string $name): mixed
    • __invoke(mixed $arguments): mixed
    • __isset(string $name): bool
    • __serialize(): array
    • __set(string $name, mixed $value): void
    • __set_state(array $properties): object
    • __sleep(): array
    • __unserialize(array $data): void
    • __unset(string $name): void
    • __wakeup(): void

  • call_user_func_array() array keys will now be interpreted as parameter names, instead of being silently ignored.

  • Declaring a function called assert() inside a namespace is no longer allowed, and issues E_COMPILE_ERROR. The assert() function is subject to special handling by the engine, which may lead to inconsistent behavior when defining a namespaced function with the same name.

Resource to Object Migration

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

COM and .Net (Windows)

The ability to import case-insensitive constants from type libraries has been removed. The second argument to com_load_typelib() may no longer be false; com.autoregister_casesensitive may no longer be disabled; case-insensitive markers in com.typelib_file are ignored.

CURL

CURLOPT_POSTFIELDS no longer accepts objects as arrays. To interpret an object as an array, perform an explicit (array) cast. The same applies to other options accepting arrays as well.

Date and Time

mktime() and gmmktime() now require at least one argument. time() can be used to get the current timestamp.

DOM

Unimplemented classes from the DOM extension that had no behavior and contained test data have been removed. These classes have also been removed in the latest version of the DOM standard:

Unimplemented methods from the DOM extension that had no behavior have been removed:

Enchant

Exif

read_exif_data() has been removed; exif_read_data() should be used instead.

Filter

GD

GMP

gmp_random() has been removed. One of gmp_random_range() or gmp_random_bits() should be used instead.

Iconv

iconv implementations which do not properly set errno in case of errors are no longer supported.

IMAP

Internationalization Functions

LDAP

MBString

OCI8

ODBC

OpenSSL

Regular Expressions (Perl-Compatible)

When passing invalid escape sequences they are no longer interpreted as literals. This behavior previously required the X modifier – which is now ignored.

PHP Data Objects

PDO ODBC

The php.ini directive pdo_odbc.db2_instance_name has been removed.

PDO MySQL

PDO::inTransaction() now reports the actual transaction state of the connection, rather than an approximation maintained by PDO. If a query that is subject to "implicit commit" is executed, PDO::inTransaction() will subsequently return false, as a transaction is no longer active.

PostgreSQL

Phar

Metadata associated with a phar will no longer be automatically unserialized, to fix potential security vulnerabilities due to object instantiation, autoloading, etc.

Reflection

Sockets

Standard PHP Library (SPL)

Standard Library

Sysvsem

Tidy

Tokenizer

XMLReader

XMLReader::open() and XMLReader::XML() are now static methods. They can still be called as instance methods, but inheriting classes need to declare them as static if they override these methods.

XML-RPC

The XML-RPC extension has been moved to PECL and is no longer part of the PHP distribution.

Zip

ZipArchive::OPSYS_Z_CPM has been removed (this name was a typo). Use ZipArchive::OPSYS_CPM instead.

Zlib

Windows PHP Test Packs

The test runner has been renamed from run-test.php to run-tests.php, to match its name in php-src.