Closures · Function

iscclosure

Returns whether the given function is a native C closure.

function iscclosure(func: function): boolean

Synopsis

How it works

Checks the Luau type tag of the closureClosureA function value that captures its lexical environment. In Luau, closures come in two types: LClosure (Luau bytecode + Proto + upvalues) and CClosure (native C function pointer + upvalues).'s internal struct. Luau closures have type LUA_TFUNCTION but two subtypes: LClosure (Luau bytecodeBytecodeThe compiled binary representation of Luau source code. A sequence of 32-bit instructions (opcodes + operands) stored in a Proto's code[] array. Executed by the Luau VM interpreter.) and CClosure (native C). This function returns true if the closure is a CClosure — meaning it was created from a lua_CFunction pointer.

What returns true

Built-in Roblox methods (print, warn, error)
Standard library functions (math.abs, string.find)
newcclosure-wrapped functions
C functions registered by the executor

Usage

Check closure type

print(iscclosure(print))             "cc">--> true
print(iscclosure(function() end))    "cc">--> false
print(iscclosure(newcclosure(function() end))) "cc">--> true

Parameters

func function

The function to inspect.

Returns

boolean true if the function is a C closure.