ROBLOX LUA(u) check arguments of a function - lua

Question

I have this function.
As you can see, I define fn to run a function with arguments provided, how can I check if the amount of arguments that the fn function receives is the amount needed for the function v? Ie, if the user provides 2 args but 3 are needed, throw an error.
ModuleScript:
-- Variables
local dss = game:GetService("DataStoreService")
local db = dss:GetDataStore("greenwich")
-- Tables
local greenwich = {}
local dbFunctions = {}
-- Functions
function greenwich:GetDB(name)
local new = {}
new.name = name
coroutine.resume(coroutine.create(function()
for k, v in pairs(dbFunctions) do
local fn = function(...)
local args = {...}
return v(unpack(new), unpack(args))
end
new[k] = fn
new[string.lower(k)] = fn
end
end))
return new
end
function dbFunctions:Set(store, key, value)
store = store.name
db:SetAsync(store .. key, value)
return value
end
function dbFunctions:Get(store, key)
store = store.name
return db:GetAsync(store .. key)
end
function dbFunctions:Delete(store, key)
store = store.name
local success, val = pcall(function()
return db:RemoveAsync(store .. key)
end)
if val and success then
return true
else
return false
end
end
function dbFunctions:Has(store, key)
store = store.name
return not not db:GetAsync(store .. key)
end
-- Returning everything.
return greenwich

Answer 1

In the standard library of Lua 5.3.5, you can use the debug.getInfo() function to inspect the function. The table that is returned contains a field called nparams which will tell you how many args the function expects.
local example = {}
function example.func(a, b, c)
print(a, b, c)
end
local info = debug.getinfo(example.func)
print(info.nparams) -- 3
In Roblox Lua, which is a custom version based on Lua 5.1, the debug library is heavily modified and you'll need to use the debug.info() function. When you pass in a function and the argument "a", it returns the arity of the function.
local example = {}
function example.funcA(a, b, c)
print(a, b, c)
end
function example:funcB(a, b, c)
print(a, b, c)
end
function example:funcC(a, b, c, ...)
print(a, b, c)
end
-- print out the number of args and whether there's a vararg
print(debug.info(example.funcA, "a")) -- 3 false
print(debug.info(example.funcB, "a")) -- 4 false
print(debug.info(example.funcC, "a")) -- 4 true