Lua and inheritance: unable to access self object in functions

Question

I am a begginner in Lua and I am trying to code inheritance.

I have done the example from here and this example is working: http://lua-users.org/wiki/ObjectOrientationTutorial

So I've done my classes trying to keep the tutorial syntax but I can't access a derived class function.

This is my code for the base class:

Controller = {page_title = "", view = "index"}
Controller.__index = Controller

setmetatable(Controller, {
__call = function (cls, ...)
  local self = setmetatable({}, cls)
  self:new(...)
  return self
end,
})

function Controller:new()
end

-- Execute the function given in parameter
function Controller:execute(functionName)        
    if(self[functionName] ~= nil) then
        self[functionName]()
    else
        ngx.say("Cette page n'existe pas")
    end
end

The code for the derived class:

require("controllers/Controller")

ControllerUser = {page_title = ""}
ControllerUser.__index = ControllerUser

setmetatable(ControllerUser, {
  __index = Controller, -- this is what makes the inheritance work
  __call = function (cls, ...)
    local self = setmetatable({}, cls)
    self:new(...)
    return self
  end,
})

function ControllerUser:new()
    Controller:new()
    ngx.say('created!') --Displayed one time
    return self
end



function ControllerUser:creerCompte()
    ngx.say("Executed!") --Displays correctly the message
    ngx.say(self.page_title) -- Error: attempt to index local 'self' (a nil value)

end

return ControllerUser

Finally the main function:

local controller = require("controllers/ControllerUsers"):new() --tried without new but it doesn't change anything

-- Call the function "creerCompte" of the class ControllerUsers (which inherits from Controller)
controller:execute("creerCompte")

Thanks in advance for any help

Unrelated, but :new() here doesn't create a new object, so you're initializing the class table as if it were an instance. — Colonel Thirty Two
– Colonel Thirty Two, Commented Sep 26, 2014 at 15:56

lisu · Accepted Answer · 2014-09-26 19:44:34Z

2

Try replacing

function Controller:execute(functionName)        
    if(self[functionName] ~= nil) then
        self[functionName]()
    else
        ngx.say("Cette page n'existe pas")
    end
end

with

function Controller:execute(functionName)        
    if(self[functionName] ~= nil) then
        self[functionName](self)
    else
        ngx.say("Cette page n'existe pas")
    end
end

answered Sep 26, 2014 at 19:44

lisu

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