WARNING: An earlier version of this post introduced a new type checking feature, generic functions. Unfortunately we found a few critical bugs in that feature and had to disable it. Expect it to resurface in the next recap!
Luau is our new language that you can read more about at Luau - Luau. It’s been a busy month in Luau!
Here’s what’s new:
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
Typechecking improvements
We’ve made various improvements to the Luau typechecker:
- Check bodies of methods whose
selfhas typeany - 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.signandmath.roundby 2.3x, 2x and 1.6x respectively - Optimized
coroutine.resumewith ~10% gains on coroutine-heavy benchmarks - Equality comparisons are now a bit faster when comparing to constants, including
nil; this makes some benchmarks 2-3% faster - Calls to builtin functions like
math.absorbit32.rrotateare now significantly faster in some cases, e.g. this makes SHA256 benchmark 25% faster -
rawset,rawget,rawequaland 2-argumenttable.insertare now 40-50% faster; notably,table.insert(t, v)is now faster thant[#t+1]=v
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!
Debugger improvements
We continue to improve our Luau debugger and we have added a new feature to help with coroutine call debugging. The call stack that is being displayed while stopped inside a coroutine frame will display the chain of threads that have called it.
Before:
After:
We have restored the ability to break on all errors inside the scripts. This is useful in cases where you need to track the location and state of an error that is triggered inside ‘pcall’. For example, when the error that’s triggered is not the one you expected.
Library changes
- Added the
debug.infofunction which allows retrieving information about stack frames or functions; similarly todebug.getinfofrom Lua, this accepts an options string that must consist of charactersslnfa; 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/orandIsA!
Time to switch all instances of table[#table+1]=value in my code to use table.insert now
