iscclosure

Tells you whether a function was written in C or in Luau.

iscclosure(func: function): boolean

Most commonly used to tell a real Roblox Instance apart from a Luau table pretending to be one - real Instance methods like Destroy are always C closures, so a Luau result means the object is a fake.

local function analyzeObject(obj)
    if type(obj.Destroy) == "function" then
        if iscclosure(obj.Destroy) then
            print("this is a raw roblox instance")
            -- interacting directly with the engine
        else
            print("this is a lua proxy/wrapper table")
            -- the game is intercepting this call
        end
    end
end

Parameters

Parameter	Type	Description
func	function	The function to check.

Returns

true if func is a C closure, false if it’s a Luau closure.

Example

Example 1

local function luaFn() end
local cFn = newcclosure(luaFn)

print(iscclosure(print)) -- true, engine C closure
print(iscclosure(cFn))   -- true, wrapped into a C closure
print(iscclosure(luaFn)) -- false, plain Luau function

C closures represent built-in engine functions or wrapped native code.