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68 lines
3.3 KiB
Markdown
68 lines
3.3 KiB
Markdown
---
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layout: single
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title: "Luau Recap: May 2021"
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---
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Luau is our new language that you can read more about at [https://roblox.github.io/luau](https://roblox.github.io/luau). This month we have added a new small feature to the language and spent a lot of time improving our typechecker.
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[Cross-posted to the [Roblox Developer Forum](https://devforum.roblox.com/t/luau-recap-may-2021/).]
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## Named function type arguments
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We've updated Luau syntax to support optional names of arguments inside function types.
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The syntax follows the same format as regular function argument declarations: `(a: number, b: string)`
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Names can be provided in any place where function type is used, for example:
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* in type aliases:
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```
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type MyCallbackType = (cost: number, name: string) -> string
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```
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* for variables:
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```
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local cb: (amount: number) -> number
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local function foo(cb: (name: string) -> ())
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```
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Variadic arguments cannot have an extra name, they are already written as ...: number.
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These names are used for documentation purposes and we also plan to display them in Roblox Studio auto-complete and type hovers.
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They do not affect how the typechecking of Luau scripts is performed.
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## Typechecking improvements
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Speaking of typechecking, we've implemented many improvements this month:
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* Typechecker will now visit bodies of all member functions, previously it didn't check methods if the self type was unknown
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* Made improvements to cyclic module import detection and error reporting
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* Fixed incorrect error on modification of table intersection type fields
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* When using an 'or' between a nillable type and a value, the resulting type is now inferred to be non-nil
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* We have improved error messages that suggest to use ':' for a method call
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* Fixed order of types in type mismatch error that was sometimes reversed
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* Fixed an issue with `table.insert` function signature
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* Fixed a bug which caused spurious unknown global errors
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We've also added new checks to our linter:
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* A new check will report uses of deprecated Roblox APIs
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* Linter will now suggest replacing globals with locals in more cases
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* New warning is generated if array loop starts or ends on index '0', but the array is indexed from '1'
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* FormatString lint will now check string patterns for `find`/`match` calls via `:` when object type is known to be a string
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We also fixed one of the sources for "Free types leaked into this module's public interface" error message and we are working to fix the remaining ones.
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As usual, typechecking improvements will not break execution of your games even if new errors get reported.
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## Editor features
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We continue to improve our built-in support for auto-complete that will be used in future Roblox Studio updates and will make it easier to implement custom extensions for applications that support Language Server Protocol.
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As part of this work we will improve the type information provided by Roblox APIs to match actual arguments and results.
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## Behavior changes
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When a relational comparison fails at runtime, the error message now specifies the comparison direction (e.g. `attempt to compare nil <= number`)
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## Performance improvements
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* Improved performance of table lookup with an index operator and a literal string: `t["name"]`
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* Bytecode compilation is now ~5% faster which can improve server startup time for games with lots of scripts
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