Immutable¶
An immutable object is an object that can’t be changed. It may be created, read and cloned. On the other hand, a mutable object may change when one of its method is called, even if this is not visible from the outside.
Immutable objects are thread-safe.
Immutable objects often return a clone version of themselves, after modification.
<?php
class x {
private $x = 0;
function inc() : self {
$return = clone $this;
$return->x +=1;
return $return;
}
}
$a = new x();
$b = $a->inc();
// $a and $b are two distinct objects
?>
See also The case for immutability, Elegant immutable object pattern in PHP
