--- /dev/null
+/**
+Convert an object with `readonly` keys into a mutable object. Inverse of `Readonly<T>`.
+
+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).
+
+@example
+```
+import {Mutable} from 'type-fest';
+
+type Foo = {
+ readonly a: number;
+ readonly b: string;
+};
+
+const mutableFoo: Mutable<Foo> = {a: 1, b: '2'};
+mutableFoo.a = 3;
+```
+*/
+export type Mutable<ObjectType> = {
+ // For each `Key` in the keys of `ObjectType`, make a mapped type by removing the `readonly` modifier from the key.
+ -readonly [KeyType in keyof ObjectType]: ObjectType[KeyType];
+};