attempt to index local 'self' using MOAICoroutine in Lua - lua

Question

I am just starting with MOAI and I am trying to create a traditional game loop using MOAICoroutine. The problem is that when I pass it the function that is part of a "class" that is built using 30log, it returns an error. It seems to continue to function, but I would like to fix the error. My guess is that the MOAICoroutine is calling the function using the dot notation rather than the syntactical sugar method with a colon. Here is the code:
class = require "30log.30log"
GameSystem = class ()
function GameSystem:__init(Name, Title)
self.Name = Name
self.Title = Title
self.Ready = false
end
function GameSystem:Run()
if self:Init() then
self.Thread = MOAICoroutine.new ()
self.Thread:run(self.Start)
--self:Start()
return true
else
print("Init failed.")
return false
end
end
function GameSystem:Init()
print("Initializing Game System")
if not self:InitTimer() then return false end
if not self:InitWindow(640,480) then return false end
if not self:InitViewport() then return false end
if not self:InitGraphics() then return false end
if not self:InitSound() then return false end
if not self:InitInput() then return false end
self.Ready = true
return true
end
function GameSystem:Start()
print("Starting Game System")
while self.Ready do
self:UpdateTimer()
self:UpdateGraphics()
self:UpdateSound()
self:UpdateInput()
coroutine.yield()
end
end
function GameSystem:InitTimer()
return true
end
function GameSystem:InitWindow(width, height)
print("Initializing Window")
return true
end
function GameSystem:InitViewport()
print("Initializing Viewport")
return true
end
function GameSystem:InitGraphics()
print("Initializing Graphics")
return true
end
function GameSystem:InitSound()
print("Initializing Sound")
return true
end
function GameSystem:InitInput()
print("Initializing Input")
return true
end
function GameSystem:UpdateTimer()
--print("Updating Timer")
return true
end
function GameSystem:UpdateGraphics()
--print("Updating Graphics")
return true
end
function GameSystem:UpdateSound()
--print("Updating Sound")
return true
end
function GameSystem:UpdateInput()
--print("Updating Input")
return true
end
Is the 30log class code causing this problem? I have tried various things. I am pretty sure the self it is trying to access is the first argument i.e. mytable.myfunction(self, myarg). Any ideas to fix this nil value reference. The error actually occurred on the second line inside the Start function (while self.Ready do).

Answer 1

function GameSystem:Run()
if self:Init() then
self.Thread = MOAICoroutine.new ()
self.Thread:run(self.Start)
My guess is that the MOAICoroutine is calling the function using the dot notation rather than the syntactical sugar method with a colon.
How would it be calling the function using dot notion (or colon notation)? What would be on the left side of the period or colon? You haven't passed it an object, only a function. The fact that it's caller was storing that function in a table is completely unknown to it. It just receives a function, and calls it.
If you want your coroutine to start with a method call, do that in the function you pass to coroutine.start:
self.Thread = MOAICoroutine.new ()
self.Thread:run(function() self:Start() end)
The point is that:
function GameSystem:Start()
end
Is exactly equivalent to:
function GameSystem.Start(self)
end
Is exactly equivalent to:
GameSystem.Start = function(self)
end
Is equivalent to:
function Foobar(self)
end
GameSystem.Start = Foobar
If I call:
print(Foobar)
print(GameSystem.Start)
print(someGameSystemInstance.Start)
print receives the same value. In Lua, a function is a function is a function, it's not "tainted" in some way by being stored in a table, such that a third party with a reference to the function can know that you want it to be called as a method to some particular 'class instance.