ExcludeRestElement: Fix generic assignability with arrays#1274
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sindresorhus merged 4 commits intomainfrom Oct 25, 2025
Merged
ExcludeRestElement: Fix generic assignability with arrays#1274sindresorhus merged 4 commits intomainfrom
ExcludeRestElement: Fix generic assignability with arrays#1274sindresorhus merged 4 commits intomainfrom
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som-sm
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Oct 17, 2025
| : [...Result[0], ...Result[2]] | ||
| : Result | ||
| : never; | ||
| : never |
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If this is Result (and not never), then the compiler thinks the type produces something more than just arrays.
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benzaria
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Oct 17, 2025
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| export type ExcludeRestElement<Array_ extends UnknownArray> = IfNotAnyOrNever<Array_, | ||
| SplitOnRestElement<Array_> extends infer Result | ||
| ? Result extends readonly UnknownArray[] | ||
| ? IsArrayReadonly<Array_> extends true | ||
| ? Readonly<[...Result[0], ...Result[2]]> | ||
| : [...Result[0], ...Result[2]] | ||
| : Result | ||
| : never; | ||
| : never | ||
| : never | ||
| >; |
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Please consider using IsAnyOrNever instead, as it provides more reliable handling for recursive types.
Refer my #1192 comment, and your #1266 comment regarding If* types.
Suggested change
| export type ExcludeRestElement<Array_ extends UnknownArray> = IfNotAnyOrNever<Array_, | |
| SplitOnRestElement<Array_> extends infer Result | |
| ? Result extends readonly UnknownArray[] | |
| ? IsArrayReadonly<Array_> extends true | |
| ? Readonly<[...Result[0], ...Result[2]]> | |
| : [...Result[0], ...Result[2]] | |
| : Result | |
| : never; | |
| : never | |
| : never | |
| >; | |
| export type ExcludeRestElement<Array_ extends UnknownArray> = | |
| IsAnyOrNever<Array_> extends true ? Array_ | |
| : SplitOnRestElement<Array_> extends infer Result | |
| ? Result extends readonly UnknownArray[] | |
| ? IsArrayReadonly<Array_> extends true | |
| ? Readonly<[...Result[0], ...Result[2]]> | |
| : [...Result[0], ...Result[2]] | |
| : never | |
| : never; |
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IfNotAnyOrNever works perfectly fine in this case because ExcludeRestElement is not a recursive type. Added test cases for long tuples in #0aed831.
your #1266 comment regarding
If*types.
This was only for recursive types.
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And, if used properly, IfNotAnyOrNever can even be used with recursive types without any problems. Added a note in #1276.
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Currently, instantiations of
ExcludeRestElementwith generic types are not assignable toreadonly unknown[], this PR fixes this issue.This issue is also related to #1166 (comment). In general, it's better to handle
anyandnevercases explicitly.