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1 | import {Except} from './except';
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2 | import {Simplify} from './simplify';
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3 |
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4 | /**
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5 | Create a type that strips `readonly` from all or some of an object's keys. Inverse of `Readonly<T>`.
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6 |
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7 | This can be used to [store and mutate options within a class](https://github.com/sindresorhus/pageres/blob/4a5d05fca19a5fbd2f53842cbf3eb7b1b63bddd2/source/index.ts#L72), [edit `readonly` objects within tests](https://stackoverflow.com/questions/50703834), [construct a `readonly` object within a function](https://github.com/Microsoft/TypeScript/issues/24509), or to define a single model where the only thing that changes is whether or not some of the keys are mutable.
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8 |
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9 | @example
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10 | ```
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11 | import {Mutable} from 'type-fest';
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12 |
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13 | type Foo = {
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14 | readonly a: number;
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15 | readonly b: readonly string[]; // To show that only the mutability status of the properties, not their values, are affected.
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16 | readonly c: boolean;
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17 | };
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18 |
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19 | const mutableFoo: Mutable<Foo> = {a: 1, b: ['2']};
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20 | mutableFoo.a = 3;
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21 | mutableFoo.b[0] = 'new value'; // Will still fail as the value of property "b" is still a readonly type.
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22 | mutableFoo.b = ['something']; // Will work as the "b" property itself is no longer readonly.
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23 |
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24 | type SomeMutable = Mutable<Foo, 'b' | 'c'>;
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25 | // type SomeMutable = {
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26 | // readonly a: number;
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27 | // b: readonly string[]; // It's now mutable. The type of the property remains unaffected.
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28 | // c: boolean; // It's now mutable.
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29 | // }
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30 | ```
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31 | */
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32 | export type Mutable<BaseType, Keys extends keyof BaseType = keyof BaseType> =
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33 | Simplify<
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34 | // Pick just the keys that are not mutable from the base type.
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35 | Except<BaseType, Keys> &
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36 | // Pick the keys that should be mutable from the base type and make them mutable by removing the `readonly` modifier from the key.
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37 | {-readonly [KeyType in keyof Pick<BaseType, Keys>]: Pick<BaseType, Keys>[KeyType]}
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38 | >;
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