Metatable, how to subtract two tables?
Hey devs! I want to make a playlist. I want make two tables.
I dont really good speak english so i make a exemple
lua
local history = {
sound1 = {'name', 0000000}
}
local list = {sound1 = {'name', 0000000},
sound2 = {'namE', 0000001},
sound4 = {'nAmE', 0000004}
}
I make a first table named history to stored the sounds already listened.
I know than I can substrac two tables if a make metatable. But I dont know how to use it correctly. Exemple of my expected result
```lua setmetatable(history, list)
function ...()
-- ??
local playlist = (history - list)
-- ??
for i, s in pairs(playlist) do
...
end
...
end
--[[
expected result:
playlist = {sound2 = {'namE', 0000001},
sound4 = {'nAmE', 0000004}
}
]]
}
```
Sorry if is not precise i don't speak english i'm french and it's hard to talk english. Thanks for anwsers
Can I create that with MetaTable?
0
1 answer
Well, you'd need to use the __sub metamethod. Here's an example I made:
```lua local t1 = {1, 2, 3, 4} local t2 = {2, 4}
local mt = {}
function mt.__sub(a, b) local function find(v) for _, value in pairs(b) do if v == value then return true end end return false end
for i,v in pairs(a) do if find(v) then table.remove(a, i) end end
return a end
function mt.__tostring(t) return table.concat(t, ',') end
t1 = setmetatable(t1, mt) t2 = setmetatable(t2, mt)
print(t1 - t2) ```
Result:
1, 3 Because we subtracted 2, and 4 from t2, from t1 which had 1-4