WordPress 5.9 changes for PHP 8 and 8.1 compatibility

WordPress 5.9 has made some changes for compatibility with PHP 8 and 8.1

WordPress 5.9 PHP changes

Although WordPress 5.9 is not fully compatible with PHP 8.0 and 8.1, below are a few changes that theme and plugin developers need to know.

array_key_first()

array_key_last()

str_contains()

str_starts_with()

str_ends_with()

readonly() function has been renamed to wp_readonly() in WordPress 5.9
Deprecated functions: date_sunrise(), date_sunset(), gmstrftime(), strftime(), strptime()
Deprecated hash functions: Hash functions: mhash(), mhash_keygen_s2k(), mhash_count(), mhash_get_block_size(), and mhash_get_hash_name() .
Calling the following on objects is deprecated: key(), current(), next(), prev(), reset(), or end()
External libraries included in WordPress 5.9 for PHP 8 and 8.1 support include;

GetID3 1.9.21

SimplePie 1.5.7

PHPMailer 6.5.1

More detailed information is available on this page: WordPress 5.9 changes PHP changes