Written once

1<?php2class Point {3    public function __construct(4        public readonly int $x,5        public readonly int $y = 0,6    ) {}7    public function withX(int $x): static {8        return new static($x, $this->y);9    }10}11$p = new Point(1, 2);12echo "$p->x,$p->y\n";13try {14    $p->x = 5;15} catch (Error $e) {16    echo $e->getMessage(), "\n";17}18$q = $p->withX(5);19echo "$q->x,$q->y / $p->x,$p->y\n";