Comment créer une classe, une sous-classe et des propriétés à Lua?

Je vais avoir du mal à grokking classes dans Lua . Un googling sans fruit m'a conduit aux idées sur les méta-tables et implicite que des bibliothèques tierces sont nécessaires pour simuler / écrire des cours.

Voici un échantillon (juste parce que j'ai remarqué que j'obtiens de meilleures réponses lorsque je fournis un code d'échantillon): p>

--Everything is a table
ElectronicDevice = {};

--Magic happens
mt = {__index=ElectronicDevice};

--This must be a constructor
function ElectronicDeviceFactory ()
    -- Seems that the metatable holds the fields
    return setmetatable ({isOn=true}, mt)
end

-- Simulate properties with get/set functions
function ElectronicDevice:getIsOn()  return self.isOn end
function ElectronicDevice:setIsOn(value)  self.isOn = value end
function ElectronicDevice:Reboot() self.isOn = false;
    self:ResetHardware(); self.isOn = true; end
function ElectronicDevice:ResetHardware()  print('resetting hardware...') end

Router = {};
mt_for_router = {__index=Router}

--Router inherits from ElectronicDevice
Router = setmetatable({},{__index=ElectronicDevice});

--Constructor for subclass, not sure if metatable is supposed to be different
function RouterFactory ()
    return setmetatable ({},mt_for_router)
end

Modem ={};
mt_for_modem = {__index=Modem}

--Modem inherits from ElectronicDevice
Modem = setmetatable({},{__index=ElectronicDevice});

--Constructor for subclass, not sure if metatable is supposed to be different
function ModemFactory ()
    return setmetatable ({},mt_for_modem)
end

function Modem:WarDialNeighborhood(areaCode)
        cisco = RouterFactory();
        --polymorphism
        cisco.Reboot(); --Call reboot on a router
        self.Reboot(); --Call reboot on a modem
        if (self.isOn) then self:StartDialing(areaCode) end;
end

function Modem:StartDialing(areaCode)
    print('now dialing all numbers in ' .. areaCode);
end

testDevice = ElectronicDeviceFactory();
print("The device is on? " .. (testDevice:getIsOn() and "yes" or "no") );
testDevice:Reboot(); --Ok

testRouter = RouterFactory();
testRouter:ResetHardware(); -- nil value

testModem = ModemFactory();
testModem:StartDialing('123'); -- nil value