i = !0
i.update! _ -> 1
i.update! i -> i * 3
assert i == 3

i.inc!()
assert i == 4
i.dec!()
assert i == 3
assert i.abs() == 3

ss = !"abc"
ss.push! "d"
assert ss == "abcd"
discard ss.pop!()
assert ss == "abc"
discard ss.remove! 0
assert ss == "bc"
assert ss.capitalize() == "Bc"