Variable or Infinite Depth Table Function

return function(_size)
    local function f(self, key, i)
        i = i or 1
        self[key] = setmetatable({}, {
            __index = i >= _size and {} or function(self2, key2)
                return f(self2, key2, _size ~= -1 and i + 1)
            end;
        })
        return self[key]
    end
    return f
end