diff --git a/docs/_posts/2022-06-01-luau-recap-may-2022.md b/docs/_posts/2022-06-01-luau-recap-may-2022.md new file mode 100644 index 00000000..e9b3e29a --- /dev/null +++ b/docs/_posts/2022-06-01-luau-recap-may-2022.md @@ -0,0 +1,102 @@ +--- +layout: single +title: "Luau Recap: May 2022" +--- + +Read more about Luau at [https://luau-lang.org](https://luau-lang.org). + +[Cross-posted to the [Roblox Developer Forum](https://devforum.roblox.com/t/luau-recap-may-2022/).] + +This month Luau team has worked to bring you a new language feature together with more typechecking improvements and bugfixes! + +## Generalized iteration + +We have extended the semantics of standard Lua syntax for iterating through containers, `for vars in values` with support for generalized iteration. +In Lua, to iterate over a table you need to use an iterator like `next` or a function that returns one like `pairs` or `ipairs`. In Luau, you can now simply iterate over a table: + +```lua +for k, v in {1, 4, 9} do + assert(k * k == v) +end +``` + +This works for tables but can also be customized for tables or userdata by implementing `__iter` metamethod. It is called before the iteration begins, and should return an iterator function like `next` (or a custom one): + +```lua +local obj = { items = {1, 4, 9} } +setmetatable(obj, { __iter = function(o) return next, o.items end }) + +for k, v in obj do + assert(k * k == v) +end +``` + +The default iteration order for tables is specified to be consecutive for elements `1..#t` and unordered after that, visiting every element. +Similar to iteration using `pairs`, modifying the table entries for keys other than the current one results in unspecified behavior. + +## Typechecking improvements + +We have added a missing check to compare implicit table keys against the key type of the table indexer: + +```lua +-- error is correctly reported, implicit keys (1,2,3) are not compatible with [string] +local t: { [string]: boolean } = { true, true, false } +``` + +Rules for `==` and `~=` have been relaxed for union types, if any of the union parts can be compared, operation succeeds: + +```lua +--!strict +local function compare(v1: Vector3, v2: Vector3?) + return v1 == v2 -- no longer an error +end +``` + +Table value type propagation now correctly works with `[any]` key type: + +```lua +--!strict +type X = {[any]: string | boolean} +local x: X = { key = "str" } -- no longer gives an incorrect error +``` + +If a generic function doesn't provide type annotations for all arguments and the return value, additional generic type parameters might be added automatically: + +```lua +-- previously it was foo, now it's foo, because second argument is also generic +function foo(x: T, y) end +``` + +We have also fixed various issues that have caused crashes, with many of them coming from your bug reports. + +## Autocomplete improvements + +Studio autocomplete has received a few improvements: + +* Function argument names have been added to the function signature display +* `Instance:GetAttribute` and `Instance:SetAttribute` will now suggest attribute names if instance can be resolved +* Inside the new if-then-else expression, incorrect suggestions following `else` have been fixed +* Deprecated lowercase `Color3:toHSV` so it's no longer suggested +* Deprecated lowercase `Instance:findFirstChild`, `Instance:clone`, `Instance:remove`, `Instance:getChildren` and old alias called `Instance:children`. + +## Linter improvements + +`global-used-as-local` lint warning has been extended to notice when global variable writes always happen before their use in a local scope, suggesting that they can be replaced with a local variable: + +```lua +function bar() + foo = 6 -- Global 'foo' is never read before being written. Consider changing it to local + return foo +end +function baz() + foo = 10 + return foo +end +``` + +## Performance improvements + +Garbage collection CPU utilization has been tuned to further reduce frame time spikes of individual collection steps and to bring different GC stages to the same level of CPU utilization. + +In open-source release of Luau, when optimization level 2 is enabled, compiler will now perform function inlining. +Loop unrolling in optimization level 2 has also been improved to handle all language constructs inside the loop body.