Lua OOP not finding variables - oop

Question

I'm trying to do OOP in Lua, but it's not letting me change the vel_y value in the checkInput{} method. Any ideas how i can get this to work? By the way I'm using Love2D for this input stuff.
Player = {x = 100, y = 20, vel_x = 0, vel_y = 0}
function Player:new(o, x, y, vel_x, vel_y)
o = o or {} -- create object if user does not provide one
setmetatable(o, self)
self.__index = self
length = 0
return o
end
function Player:getX()
return self.x
end
function Player:getY()
return self.y
end
function Player:update( dt )
--update velocity
self.x = self.x + self.vel_x
self.y = self.y + self.vel_y
checkInput()
end
function checkInput( dt )
if love.keyboard.isDown("w") and length < 5 then --press the right arrow key to push the ball to the right
length = length + 1
self.vel_y = 5
print("bruhddddddddddddddddddddddd")
elseif love.keyboard.isDown("a") then
elseif love.keyboard.isDown("s") then
elseif love.keyboard.isDown("d") then
end
end

Answer 1

I assume your system call player:update() firs? If so you should pass self and dt to checkInput
function Player:update( dt )
--update velocity
self.x = self.x + self.vel_x
self.y = self.y + self.vel_y
checkInput(self, dt) --<--
end
...
function checkInput( self, dt )
...
if you define checkInput as local (of course before Player:update) this may be similar to private method.
Player = {x = 100, y = 20, vel_x = 0, vel_y = 0} do
Player.__index = self -- we can do this only once
function Player:new(o, x, y, vel_x, vel_y)
o = setmetatable(o or {}, self) -- create object if user does not provide one
-- init o here
return o
end
function Player:getX() end
function Player:getY() end
-- Private method
local function checkInput(self, dt) end
function Player:update( dt )
...
checkInput(self, dt) -- call private method
end
end -- end clsss defenitioin