Closures

The closure functions are used to create, identify, and interact with Luau closures.

---

checkcaller

function checkcaller(): boolean

Returns whether the function currently running was called by the executor.

This is useful for metamethod hooks that behave differently when called by the game.

Example

Prevent the executor from invoking __namecall with the global game object:

local refs = {}

refs.__namecall = hookmetamethod(game, "__namecall", function(...)
	local self = ...
	local isRunningOnExecutor = checkcaller()

	if isRunningOnExecutor then
		-- The executor invoked the __namecall method, so this will not affect the
		-- scripts in the game.
		if self == game then
			error("No __namecall on game allowed")
		end
	end

	return refs.__namecall(...)
end)

game:Destroy() --> Error "No __namecall on game allowed"

---

clonefunction

clonefunction<T>(func: T): T

Generates a new closure based on the bytecode of function func.

Parameters

• func - The function to recreate.

Example

local function foo()
	print("Hello, world!")
end

local bar = clonefunction(foo)

foo() --> Hello, world!
bar() --> Hello, world!
print(foo == bar) --> false

---

getcallingscript

function getcallingscript(): BaseScript

Returns the script responsible for the currently running function.

Example

Prevent scripts in PlayerGui from invoking the __namecall hook:

local refs = {}
local bannedScripts = game:GetService("Players").LocalPlayer.PlayerGui

refs.__namecall = hookmetamethod(game, "__namecall", function(...)
	local caller = getcallingscript()

	-- Use '.' notation to call the IsDescendantOf method without invoking
	-- __namecall and causing a recursive loop.
	local isBanned = caller.IsDescendantOf(caller, bannedScripts)

	if isBanned then
		error("Not allowed to invoke __namecall")
	end

	return refs.__namecall(...)
end)

---

hookfunction

function hookfunction<T>(func: T, hook: function): T

Replaces func with hook internally, where hook will be invoked in place of func when called.

Returns a new function that can be used to access the original definition of func.

⚠️ Warning

If func is a Luau function (islclosure(func) --> true), the upvalue count of hook must be less than or equal to that of func. Read more about upvalues on Lua visibility rules.

Parameters

• func - The function to hook.

• hook - The function to redirect calls to.

Aliases

• replaceclosure

Example

local function foo()
	print("Hello, world!")
end

local fooRef = hookfunction(foo, function(...)
	print("Hooked!")
end)

foo() --> Hooked!
fooRef() --> Hello, world!

---

iscclosure

function iscclosure(func: function): boolean

Returns whether or not func is a closure whose source is written in C.

Parameters

• func - The function to check.

Example

print(iscclosure(print)) --> true
print(iscclosure(function() end)) --> false

---

islclosure

function islclosure(func: function): boolean

Returns whether or not func is a closure whose source is written in Luau.

Parameters

• func - The function to check.

Example

print(islclosure(print)) --> false
print(islclosure(function() end)) --> true

---

isexecutorclosure

function isexecutorclosure(func: function): boolean

Returns whether or not func was created by the executor.

Parameters

• func - The function to check.

Aliases

• checkclosure

• isourclosure

Example

print(isexecutorclosure(isexecutorclosure)) --> true
print(isexecutorclosure(function() end)) --> true
print(isexecutorclosure(print)) --> false

---

loadstring

function loadstring(source: string, chunkname: string?): (function?, string?)

Generates a chunk from the given source code. The environment of the returned function is the global environment.

If there are no compilation errors, the chunk is returned by itself; otherwise, it returns nil plus the error message.

chunkname is used as the chunk name for error messages and debug information. When absent, it defaults to a random string.

⛔ Danger

Vanilla Lua allows source to contain Lua bytecode, but it is a security vulnerability. This is a feature that should not be implemented.

Parameters

• source - The source code to compile.

• chunkname - Optional name of the chunk.

Example

local func, err = loadstring("print('Hello, world!')")
assert(func, err)() --> Hello, world!

local func, err = loadstring("print('Hello")
assert(func, err)() --> Errors "Malformed string"

---

newcclosure

function newcclosure<T>(func: T): T

Returns a C closure that wraps func. The result is functionally identical to func, but identifies as a C closure, and may have different metadata.

⚠️ Warning

Attempting to yield inside a C closure will throw an error. Instead, use the task library to defer actions to different threads.

Parameters

• func - The function to wrap.

Example

local foo = function() end
local bar = newcclosure(foo)

print(iscclosure(foo)) --> false
print(iscclosure(bar)) --> true