Backward Incompatible Changes
PHP Core
Array-style access of non-arrays
Trying to use values of type null, bool,
int, float or resource as an
array (such as $null["key"]) will now generate a notice.
fn keyword
fn is now a reserved keyword. In particular,
it can no longer be used as a function or class name.
It can still be used as a method or class constant name.
<?php tag at end of file
<?php at the end of the file (without trailing newline)
will now be interpreted as an opening PHP tag. Previously it was interpreted
either as a short opening tag followed by literal php and
resulted in a syntax error (with short_open_tag=1)
or was interpreted as a literal <?php string
(with short_open_tag=0).
Serialization
The o serialization format has been removed.
As it is never produced by PHP, this may only break unserialization of
manually crafted strings.
Password algorithm constants
Password hashing algorithm identifiers are now nullable strings rather
than integers.
Applications correctly using the constants PASSWORD_DEFAULT,
PASSWORD_BCRYPT, PASSWORD_ARGON2I, and PASSWORD_ARGON2ID will continue to
function correctly.
htmlentities() will now raise a notice
(instead of a strict standards warning) if it is used with
an encoding for which only basic entity substitution is supported,
in which case it is equivalent to htmlspecialchars().
fread() and fwrite() will now
return false if the operation failed.
Previously an empty string or 0 was returned.
EAGAIN/EWOULDBLOCK are not considered failures.
These functions now also raise a notice on failure,
such as when trying to write to a read-only file resource.
BCMath Arbitrary Precision Mathematics
BCMath functions will now warn if a non well-formed number is passed, such
as "32foo". The argument will be interpreted as zero, as before.
CURL
Attempting to serialize a CURLFile class will now
generate an exception. Previously the exception was only thrown on unserialization.
Using CURLPIPE_HTTP1 is deprecated, and is no longer
supported as of cURL 7.62.0.
The $version parameter of curl_version()
is deprecated. If any value not equal to the default CURLVERSION_NOW
is passed, a warning is raised and the parameter is ignored.
Date and Time
Calling var_dump() or similar on a
DateTime or DateTimeImmutable
instance will no longer leave behind accessible properties on the object.
Comparison of DateInterval objects
(using ==, <, and so on) will now generate
a warning and always return false. Previously all DateInterval
objects were considered equal, unless they had properties.
MySQLi
The embedded server functionality has been removed. It was broken since
at least PHP 7.0.
The undocumented mysqli::$stat property has been removed
in favor of mysqli::stat().
OpenSSL
The openssl_random_pseudo_bytes() function will now
throw an exception in error situations, similar to random_bytes().
In particular, an Error is thrown if the number of
requested bytes is less than or equal to zero, and an Exception
is thrown if sufficient randomness cannot be gathered.
The $crypto_strong output argument is guaranteed to always
be true if the function does not throw, so explicitly checking it is not necessary.
Regular Expressions (Perl-Compatible)
When PREG_UNMATCHED_AS_NULL mode is used, trailing
unmatched capturing groups will now also be set to null (or
[null, -1] if offset capture is enabled).
This means that the size of the $matches will always be the same.
PHP Data Objects
Attempting to serialize a PDO or
PDOStatement instance will now generate
an Exception rather than a PDOException,
consistent with other internal classes which do not support serialization.
Reflection
Reflection objects will now generate an exception if an attempt is made
to serialize them. Serialization for reflection objects was never
supported and resulted in corrupted reflection objects. It has been
explicitly prohibited now.
The values of the class constant of ReflectionClassConstant,
ReflectionMethod and ReflectionProperty
have changed.
Incoming Cookies
As of PHP 7.4.11, the names of incoming cookies are no
longer url-decoded for security reasons.
