my Int $x = 17;
my Int $y is readonly := $x;

##</code><code>##

sub foo (Int $y) { ... } 
my Int $x = 17;
foo($x);

##</code><code>##

my Int $x = 17;
$x -> $y { ... }

##</code><code>##

my Int $x is readonly = 17;
my Int $y := $x;

##</code><code>##

sub foo (Int $y is rw) { ... }
foo(17);
my Int $x is readonly = 17;
foo($x);

##</code><code>##

sub foo (Int|constInt $y) { ... }