<?php

class Foo {
  private final function __clone() {
    var_dump(__METHOD__);
  }
}

class Bar extends Foo {
}

$x = new Bar();
$_ = clone $x;

PHP: runtime error: Call to private Foo::__clone()
KPHP: no errors, default (?) cloning is performed

The final private __clone is a trick to make objects non-cloneable.

Note: even if we make the __clone() public (final is irrelevant), it's not going to be called from the derived objects.

<?php

class Foo {
  public function __clone() {
    var_dump(__METHOD__);
  }
}

class Bar extends Foo {}
class Baz extends Bar {}

$x = new Baz();
$_ = clone $x;

PHP: prints "Foo::__clone"
KPHP: prints nothing