Online PHP editor | output for TZk8B

<?php # Acknowledging Stas Malyshev # https://phabricator.wikimedia.org/T156364#2977719 # Given two classes with the same property name but different visibility class WithPublic { public $property; function __construct( $p ) { $this->property = $p; } function getProperty() { print $this->property; } } class WithPrivate { private $property; function __construct( $p ) { $this->property = $p; } function getProperty() { print $this->property; } } $pub = new WithPublic( 'value' ); # Lets pretend it is held in a permanent cache: $cache = serialize( $pub ); # Later on NEW code is deployed which change the property signature to private. # Simulate the class changed: $mut_pub_to_priv = unserialize( str_replace( '10:"WithPublic"', '11:"WithPrivate"', $cache ) ); var_dump( $mut_pub_to_priv ); # class WithPrivate#2 (2) { # private $property => # NULL # public $property => # string(5) "value" # } var_export( $mut_pub_to_priv->getProperty() ); # NULL # The object restored from cache is not quite the one we expected and cause # some havoc ( https://phabricator.wikimedia.org/T156364 ). Then Zend and HHVM # consistently yield "NULL". # The other way around. Cache with private property restore to class with # public property $priv = new WithPrivate( 'value' ); $cache = serialize( $priv ); $mut_priv_to_pub = unserialize( str_replace( '11:"WithPrivate"', '10:"WithPublic"', $cache) ); var_dump( $mut_priv_to_pub ); # class WithPublic#4 (2) { # public $property => # NULL # private $property => # string(5) "value" # } var_export( $mut_priv_to_pub->getProperty() ); # On Zend PHP: NULL # On HHVM 3.15.4, 3.17.1: valueNULL