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96 lines
3 KiB
Markdown
96 lines
3 KiB
Markdown
---
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layout: single
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title: "Luau Recap: November 2022"
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---
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While the team is busy to bring some bigger things in the future, we have made some small improvements this month.
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[Cross-posted to the [Roblox Developer Forum](https://devforum.roblox.com/t/luau-recap-november-2022/).]
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## Analysis improvements
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We have improved tagged union type refinements to only include unhandled type cases in the `else` branch of the `if` statement:
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```lua
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type Ok<T> = { tag: "ok", value: T }
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type Err = { tag: "error", msg: string }
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type Result<T> = Ok<T> | Err
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function unwrap<T>(r: Result<T>): T?
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if r.tag == "ok" then
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return r.value
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else
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-- Luau now understands that 'r' here can only be the 'Err' part
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print(r.msg)
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return nil
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end
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end
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```
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For better inference, we updated the definition of `Enum.SomeType:GetEnumItems()` to return `{Enum.SomeType}` instead of common `{EnumItem}` and the return type of `next` function now includes the possibility of key being `nil`.
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Finally, if you use `and` operator on non-boolean values, `boolean` type will no longer be added by the type inference:
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```lua
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local function f1(a: number?)
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-- 'x' is still a 'number?' and doesn't become 'boolean | number'
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local x = a and 5
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end
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```
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## Error message improvements
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We now give an error when built-in types are being redefined:
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```lua
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type string = number -- Now an error: Redefinition of type 'string'
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```
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We also had a parse error missing in case you forgot your default type pack parameter value. We accepted the following code silently without raising an issue:
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```lua
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type Foo<T... = > = nil -- Now an error: Expected type, got '>'
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```
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Error about function argument count mismatch no longer points at the last argument, but instead at the function in question.
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So, instead of:
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```lua
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function myfunction(a: number, b:number) end
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myfunction(123)
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~~~
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```
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We now highlight this:
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```lua
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function myfunction(a: number, b:number) end
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myfunction(123)
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~~~~~~~~~~
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```
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If you iterate over a table value that could also be `nil`, you get a better explanation in the error message:
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```lua
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local function f(t: {number}?)
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for i,v in t do -- Value of type {number}? could be nil
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--...
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end
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end
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```
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Previously it was `Cannot call non-function {number}?` which was confusing.
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And speaking of confusing, some of you might have seen an error like `Type 'string' could not be converted into 'string'`.
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This was caused by Luau having both a primitive type `string` and a table type coming from `string` library. Since the way you can get the type of the `string` library table is by using `typeof(string)`, the updated error message will mirror that and report `Type 'string' could not be converted into 'typeof(string)'`.
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Parsing now recovers with a more precise error message if you forget a comma in table constructor spanning multiple lines:
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```lua
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local t = {
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a = 1
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b = 2 -- Expected ',' after table constructor element
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c = 3 -- Expected ',' after table constructor element
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}
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```
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