Error when attempting to call function in different lua file (function is a nil value)

Question

I get the following error when I attempt to use call a function in a box collider object I'm trying to make.

The Error:

main.lua:26: attempt to call field 'Update' ( a nil value )

Traceback

main.lua:26: in function 'update' [C]: in function 'xpcall'

The Code:

main.lua

require("BoxCollider")

local s1 = {}
s1.x = 10
s1.y = 10
s1.w = 10
s1.h = 10
s1.collider = BoxCollider.new(s1.x,s1.y,s1.w,s1.h)

test = BoxCollider.new(40, 7,15,15)

function love.load()

end

function love.update(dt)

if love.keyboard.isDown("d") then s1.x = s1.x + 100 * dt end    
---[[   
s1.collider:Update(s1.x,s1.y)

if s1.collider:CheckCollisions(test) then
    s1.x = 10
end
--]]
end

function love.draw()

love.graphics.rectangle("fill", s1.x, s1.y, s1.w, s1.h)
love.graphics.rectangle("fill", 40, 7, 15,15)

end

BoxCollider.lua

BoxCollider = {}
BoxCollider._index = BoxCollider


--x is the x point of the collider, should be equal to the object's x point if the box        is for an object
--y is the y point of the collider, should be equal to the object's x point if the box is for an object
--w is the width of the box
--h is the height of the box

function BoxCollider.new(x,y,w,h)
return setmetatable({x = x or 0, y = y or 0, w = w or 0, h = h or 0},BoxCollider)
end

function BoxCollider:CheckCollisions( v )

return self.x < (v.x + v.h) and  v.x < (self.x + self.w) and self.y  < (v.y+v.h) and v.y < (self.y+self.h)  

end

function BoxCollider:reSize(nw,nh)
self.w = nw
self.h = nh

end

function BoxCollider:Update(nx,ny)
self.x = nx
self.y = ny
end

Answer 1

I think you just forgot an extra underscore in the BoxCollider.__index. With only one underscore, ._index, the BoxCollider methods are not being searched when :Update is called and it isn't found.