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39 lines
1.3 KiB
39 lines
1.3 KiB
// Helper type. Not useful on its own. |
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type Without<FirstType, SecondType> = {[KeyType in Exclude<keyof FirstType, keyof SecondType>]?: never}; |
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/** |
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Create a type that has mutually exclusive properties. |
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This type was inspired by [this comment](https://github.com/Microsoft/TypeScript/issues/14094#issuecomment-373782604). |
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This type works with a helper type, called `Without`. `Without<FirstType, SecondType>` produces a type that has only keys from `FirstType` which are not present on `SecondType` and sets the value type for these keys to `never`. This helper type is then used in `MergeExclusive` to remove keys from either `FirstType` or `SecondType`. |
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@example |
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``` |
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import {MergeExclusive} from 'type-fest'; |
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interface ExclusiveVariation1 { |
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exclusive1: boolean; |
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} |
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interface ExclusiveVariation2 { |
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exclusive2: string; |
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} |
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type ExclusiveOptions = MergeExclusive<ExclusiveVariation1, ExclusiveVariation2>; |
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let exclusiveOptions: ExclusiveOptions; |
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exclusiveOptions = {exclusive1: true}; |
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//=> Works |
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exclusiveOptions = {exclusive2: 'hi'}; |
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//=> Works |
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exclusiveOptions = {exclusive1: true, exclusive2: 'hi'}; |
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//=> Error |
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``` |
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*/ |
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export type MergeExclusive<FirstType, SecondType> = |
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(FirstType | SecondType) extends object ? |
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(Without<FirstType, SecondType> & SecondType) | (Without<SecondType, FirstType> & FirstType) : |
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FirstType | SecondType; |
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