Classes and modules and Lua, oh my - class

Question

I'm working on a game in Lua, and so far I have everything working with everything in one document. However, to better organize everything, I've decided to expand it into modules, and while I figure I could probably get it working more or less the same, I figure now might be an opportunity to make things a little more clear and elegant.
One example is enemies and enemy movement. I have an array called enemyTable, and here is the code in Update that moves each enemy:
for i, bat in ipairs(enemyTable) do
if bat.velocity < 1.1 * player.maxSpeed * pxPerMeter then
bat.velocity = bat.velocity + 1.1 * player.maxSpeed * pxPerMeter * globalDelta / 10
end
tempX,tempY = math.normalize(player.x - bat.x,player.y - bat.y)
bat.vectorX = (1 - .2) * bat.vectorX + (.2) * tempX
bat.vectorY = (1 - .2) * bat.vectorY + (.2) * tempY
bat.x = bat.x + (bat.velocity*bat.vectorX - player.velocity.x) * globalDelta
bat.y = bat.y + bat.velocity * bat.vectorY * globalDelta
if bat.x < 0 then
table.remove(enemyTable,i)
elseif bat.x > windowWidth then
table.remove(enemyTable,i)
end
end
This code does everything I want it to, but now I want to move it into a module called enemy.lua. My original plan was to create a function enemy.Move() inside enemy.lua that would do this exact thing, then return the updated enemyTable. Then the code inside main.lua would be something like:
enemyTable = enemy.Move(enemyTable)
What I'd prefer is something like:
enemyTable.Move()
...but I'm not sure if there's any way to do that in Lua? Does anyone have any suggestions for how to accomplish this?

Answer 1

Sounds like you just want the metatable of enemyTable to be the enemy module table. Lua 5.1 reference manual entry for metatables
Something like this.
enemy.lua
local enemy = {}
function enemy:move()
for _, bat in ipairs(self) do
....
end
end
return enemy
main.lua
local enemy = require("enemy")
enemyTable = setmetatable({}, {__index = enemy})
table.insert(enemyTable, enemy.new())
table.insert(enemyTable, enemy.new())
table.insert(enemyTable, enemy.new())
enemyTable:move()

Answer 2

Of course you can do it. For what I can see, your Move function processes the table you pass it as an argument and returns another table, in a functional programming fashion, leaving the first table immutate. You just have to set your Move function so that it knows it has to operate on your enemy table instead of creating a new table. So in your module write:
local enemy = {}
-- insert whatever enemy you want in the enemy table
function enemy.Move()
for _, bat in ipairs(enemy) do
--operate on each value of the enemy table
end
--note that this function doesn't have to return anything: not a new enemy table, at least
end
return enemy
And in your love.load function you can call
enemyTable = require "enemymodule"
Then you just have to call enemyTable.Move()