Lua, is this possible? - lua

Question

I am working on a game using love2d and i haven't quite programmed in lua. Not sure on technical wording so i'll post my code and explain what i'm trying to do:
item = {}
item.stat = {}
player.x = 100
player.y = 100
--
item[0].stat.damage = 10
What i'm trying to do is make an inventory system and an item database. I want to be able to make the item database with the code above so i could add an item like so:
item[1].stat.damage = 10
item[1].stat.speed = 10
item[2].stat.damage = 20
item[2].stat.speed = 5
--
player.inventory[0] = item[1]
player.inventory[1] = item[2]
can someone tell me what coding principle this may so i can research it? I basically want to make a matrix that i can access like above while having the convenience of named arrays instead of saying item[1,"damage"] = 10
Edit:
I realise now i can do item.stat.damage[1] = 10 but i have to setup an array for each one, is there an easier way?

Answer 1

Simply use tables:
player = {}
player.x = 100
print(player.x) -- prints 100
Note that player.x is simply syntactic sugar for player["x"], so the following lines are equivalent:
print(player.x) -- prints 100
print(player["x"]) -- also prints 100
With that in mind, you could construct your game data like this for example:
item = {}
item[1] = {}
item[1].stat = {}
item[1].stat.damage = 10
item[1].stat.speed = 10
item[2] = {}
item[2].stat = {}
item[2].stat.damage = 20
item[2].stat.speed = 5
player = {}
player.x = 100
player.y = 100
player.inventory = {}
player.inventory[1] = item[1]
player.inventory[2] = item[2]
print(player.inventory[2].stat.damage) -- prints 20
print(player["inventory"][2]["stat"]["damage"]) -- equivalent, also prints 20
It is probably a good idea to define functions that create items or players and automatically set all the required fields.
Eventually, you may want to use actual classes and objects (for example, if you want to define methods on your objects).
EDIT:
Here is the example from above with functions create_item, create_player to create items or players. I've used named parameters for these functions so one doesn't have to remember the order of the function parameters (note the curly braces when calling the functions).
function create_item(arg)
local item = {}
item.stat = {}
item.stat.damage = arg.damage
item.stat.speed = arg.speed
return item
end
function create_player(arg)
local player = {}
player.x = arg.x
player.y = arg.y
player.inventory = {}
return player
end
item = {}
item[1] = create_item{damage=10, speed=10}
item[2] = create_item{damage=20, speed=5}
player = create_player{x=100, y=100}
player.inventory[1] = item[1]
player.inventory[2] = item[2]
print(player.inventory[2].stat.damage) -- prints 20
print(player["inventory"][2]["stat"]["damage"]) -- equivalent, also prints 20

Answer 2

You can always shorten your code:
item = {
stat = {},
[0] = { stat = { damage = 10 } },
[1] = { stat = { damage = 10, speed = 10 } },
[2] = { stat = { damage = 20, speed = 5 } },
}
player = { x = 100, y = 100, inventory = { [0] = item[1], [1] = item[2] } }
You can access that code in matrix way like
function item:getstat(index, param)
return self[index] and self[index].stat and self[index].stat[param];
end
function item:setstat(index, param, value)
local t1 = self[index]
if (t1 == nil) then
t1 = {}
self[index] = t1
end
local t2 = t1.stat
if (t2 == nil) then
t2 = {}
t1.stat = t2
end
t2[param] = value
end
print(item:getstat(0, "damage"))
item:setstat(1, "speed", 20)