luau/docs/_posts/2021-03-29-luau-recap-march-2021.md

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single	Luau Recap: March 2021

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

[Cross-posted to the Roblox Developer Forum.]

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

Luau has always supported type inference for generic functions, for example:

type Point<X,Y> = { x: X, y: Y }
function swap(p)
  return { x = p.y, y = p.x }
end
local p : Point<number, string> = swap({ x = "hi", y = 37 })
local q : Point<boolean, string> = swap({ x = "hi", y = true })

but up until now, there's been no way to write the type of swap, since Luau didn't have type parameters to functions (just regular old data parameters). Well, now you can:

function swap<X, Y>(p : Point<X, Y>): Point<Y, X>
  return { x = p.y, y = p.x }
end

Generic functions can be used in function declarations, and function types too, for example

type Swapper = { swap : <X, Y>(Point<X, Y>) -> Point<Y, X> }

Typechecking improvements

We've made various improvements to the Luau typechecker:

• Check bodies of methods whose self has type any
• More precise types for debug.* methods
• Mutually dependent type aliases are now handled correctly

Performance improvements

We are continuing to squeeze the performance out of all sorts of possible code; this is an ongoing process and we have many improvements in the pipeline, big and small. These are the changes that are already live:

• 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

Note that we work off a set of benchmarks that we consider representative of the wide gamut of code that runs on Luau. If you have code that you think should be running faster, never hesitate to open a feature request / bug report on Roblox Developer Forum!

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!


Coming soon...

• Generic variadics!
• Native Vector3 math with dramatic performance improvements!
• Better tools for memory analysis!
• Better treatment of cyclic requires during type checking!
• Better type refinements including nil-ability checks, and/or and IsA!