local t = {
    a = {
        b = {
            c = {}
        }
    }
}
local t1 = t:clone(1)
assert(t1.a == t.a)      -- depth 1 does not copy nested tables
local t2 = t:clone(2)
assert(t2.a != t.a)      -- 'a' is cloned
assert(t2.a.b == t.a.b)  -- but 'b' is shared