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Fix string length type function example in Luau blog post

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Erica Marigold 2024-10-29 18:07:17 +05:30 committed by GitHub
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17
src/content/posts/luau-for-js-devs/index.md
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@ -60,21 +60,22 @@ localeFn("en-gb") // TypeError: Argument of type 'string' is not assignable to p
``` ```
```luau ```luau
type function IsStringOfLength(s: string, length: number) type function IsStringOfLength(s, length)
if #s ~= length then local lenNum = tonumber(len:value())
assert(s:is("singleton") and typeof(s:value()) == "string", "s must be of type string")
assert(len:is("singleton") and lenNum ~= nil, "len must be of type number")
if #s:value() ~= lenNum then
return error("Expected country code to be 2 characters") return error("Expected country code to be 2 characters")
end end
return s return s
end end
type LocaleCountryCode<T> = IsStringOfLength<T, 2> type LocaleCountryCode<T> = IsStringOfLength<T, "2">
local function localeFn<T>(code: LocaleCountryCode<T>)
-- Do something
end
localeFn("gb") -- This is fine local gb: LocaleCountryCode<"gb"> -- This is fine
localeFn("en-gb") -- TypeError: Expected country code to be 2 characters local enGb: LocaleCountryCode<"en-gb"> -- TypeError: Expected country code to be 2 characters
``` ```
The Luau implementation in the form of a type function is not only more readable and intuitive, it also allows for entirely customizable error diagnostics. Such a pattern is common in Luau's type system design, which emphasizes on types not overshadowing code or requiring a pHD to write due to complexity. The Luau implementation in the form of a type function is not only more readable and intuitive, it also allows for entirely customizable error diagnostics. Such a pattern is common in Luau's type system design, which emphasizes on types not overshadowing code or requiring a pHD to write due to complexity.