local M= {}
local private= {} -- holds private data of all objecs in subtables

-- Class Point: --
-- ...

-- CLASS MovablePoint: --

local MovablePoint_proto= {} -- Class prototype
function MovablePoint_proto:move(dx, dy)
    local priv= private[self]
    priv.x= priv.x+dx
    priv.y= priv.y+dy
end
MovablePoint_proto.__index   = MovablePoint_proto
MovablePoint_proto.__newindex= Point_proto.__newindex

setmetatable(MovablePoint_proto, Point_proto) -- Inherit from Point

function M.new_MovablePoint(x,y) -- constructor
    local instance= M.new_Point(x,y) -- call parent constructor
    setmetatable(instance, MovablePoint_proto)
    return instance
end

return M