Readonly¶
A property can be declared with the readonly modifier, which prevents modification of the property after initialization.
Readonly also applies inside the __clone() magic method: cloning doesn’t allow for changing a readonly property.
A class may be readonly since version 8.2, making all of of its properties readonly too.
<?php
class Test {
public readonly string $prop;
public function __construct(string $prop) {
// Legal initialization.
$this->prop = $prop;
}
}
$test = new Test(foobar);
// Legal read.
var_dump($test->prop); // string(6) foobar
// Illegal reassignment. It does not matter that the assigned value is the same.
$test->prop = foobar;
// Error: Cannot modify readonly property Test::$prop
?>
See also PHP 8.1: Readonly Properties and The Hidden Surprises of PHP Readonly Properties.
Related : Class, __clone() Method, Properties, Clone, Property Type Declaration, Var, Writeable
Added in PHP 8.1
