---
layout: single
title:  "Luau Recap: March 2021"
---

Luau is our new language that you can read more about at [https://roblox.github.io/luau](https://roblox.github.io/luau). It's been a busy month in Luau!

[Cross-posted to the [Roblox Developer Forum](https://devforum.roblox.com/t/luau-recap-march-2021/).]

## Typed variadics

Luau supports *variadic* functions, meaning ones which can take a variable number of arguments (varargs!) but previously there was no way to specify their type. Now you can!
```
function f(x: string, ...: number)
  print(x)
  print(...)
end
f("hi")
f("lo", 5, 27)
```
This function takes a string, plus as many numbers as you like, but if you try calling it with anything else, you'll get a type error, for example `f("oh", true)` gives an error " Type `boolean` could not be converted into `number`"

Variadics can be used in function declarations, and function types, for example
```
type T = {
  sum: (...number) -> number
}
function f(x: T)
  print(x.sum(1, 2, 3))
end
```

## Generic functions

[TODO]

## Typechecking improvements

* Check bodies of methods whose `self` has type `any`
* More precise types for `debug.*` methods
* Better typechecking for `Instance:IsA`.

## Performance improvements

* Significantly optimized non-variadic function calls, improving performance by up to 10% on call-heavy benchmarks
* Improve performance of `math.clamp`, `math.sign` and `math.round` by 2.3x, 2x and 1.6x respectively
* Optimized `coroutine.resume` with ~10% gains on coroutine-heavy benchmarks

## Library changes

* Added the `debug.info` function which allows retrieving information about stack frames or functions; similarly to `debug.getinfo` from Lua, this accepts an options string that must consist of characters `slnfa`; unlike Lua that returns a table, the function returns all requested values one after another to improve performance.

## New logo

Luau now has a shiny new logo!

!["New logo!"]({{ site.url }}{{ site.baseurl }}/assets/images/luau.png)

## Coming soon...

* Generic variadics!
* Better treatment of cyclic requires!
* [Anything else?]