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1 | // TODO: Remove this when we target TypeScript >=3.5.
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2 | type _Omit<T, K extends keyof any> = Pick<T, Exclude<keyof T, K>>;
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3 |
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4 | /**
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5 | 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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6 |
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7 | Use-cases:
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8 | - Creating interfaces for components that only need one of the keys to display properly.
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9 | - Declaring generic keys in a single place for a single use-case that gets narrowed down via `RequireExactlyOne`.
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10 |
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11 | 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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12 |
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13 | @example
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14 | ```
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15 | import {RequireExactlyOne} from 'type-fest';
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16 |
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17 | type Responder = {
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18 | text: () => string;
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19 | json: () => string;
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20 | secure: boolean;
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21 | };
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22 |
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23 | const responder: RequireExactlyOne<Responder, 'text' | 'json'> = {
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24 | // Adding a `text` key here would cause a compile error.
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25 |
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26 | json: () => '{"message": "ok"}',
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27 | secure: true
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28 | };
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29 | ```
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30 | */
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31 | export type RequireExactlyOne<ObjectType, KeysType extends keyof ObjectType = keyof ObjectType> =
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32 | {[Key in KeysType]: (
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33 | Required<Pick<ObjectType, Key>> &
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34 | Partial<Record<Exclude<KeysType, Key>, never>>
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35 | )}[KeysType] & _Omit<ObjectType, KeysType>;
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