siddhant@siddhant-laptop:~/perl6 code$ cat class-point
use v6;

class Point {
	has $.x;
	has $.y;
	has $.d;

	method distance_from_origin {
		$!d = sqrt($!x**2 + $!y**2);
	}
}

my $A = Point.new;

$A.x = 1;
$A.y = 2;

say $A.distance_from_origin;
siddhant@siddhant-laptop:~/perl6 code$ perl6 class-point
Cannot assign to a readonly variable or a value
  in block <anon> at class-point:1