Convert an object with `readonly` properties into a mutable object. Inverse of `Readonly<T>`.
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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), and [construct a `readonly` object within a function](https://github.com/Microsoft/TypeScript/issues/24509).
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@example
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```
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import {Mutable} from 'type-fest';
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type Foo = {
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readonly a: number;
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readonly b: string;
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};
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const mutableFoo: Mutable<Foo> = {a: 1, b: '2'};
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mutableFoo.a = 3;
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```
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*/
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exporttype Mutable<ObjectType> = {
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// For each `Key` in the keys of `ObjectType`, make a mapped type by removing the `readonly` modifier from the property.
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-readonly [KeyType in keyof ObjectType]: ObjectType[KeyType];