// TODO: Remove this when we target TypeScript >=3.5.
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type _Omit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>;
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/**
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Create a type that requires exactly one of the given keys and disallows more. The remaining keys are kept as is.
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Use-cases:
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- Creating interfaces for components that only need one of the keys to display properly.
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- Declaring generic keys in a single place for a single use-case that gets narrowed down via `RequireExactlyOne`.
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The caveat with `RequireExactlyOne` is that TypeScript doesn't always know at compile time every key that will exist at runtime. Therefore `RequireExactlyOne` can't do anything to prevent extra keys it doesn't know about.
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@example
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```
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import {RequireExactlyOne} from 'type-fest';
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type Responder = {
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text: () => string;
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json: () => string;
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secure: boolean;
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};
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const responder: RequireExactlyOne<Responder, 'text' | 'json'> = {
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// Adding a `text` key here would cause a compile error.
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json: () => '{"message": "ok"}',
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secure: true
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};
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```
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*/
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export type RequireExactlyOne<ObjectType, KeysType extends keyof ObjectType = keyof ObjectType> =
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{[Key in KeysType]: (
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Required<Pick<ObjectType, Key>> &
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Partial<Record<Exclude<KeysType, Key>, never>>
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)}[KeysType] & _Omit<ObjectType, KeysType>;
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