Type Alias Mutable<T>

Mutable: { -readonly [P in keyof T]: T[P] }

Makes all properties of an object type T mutable by removing the readonly modifier. This utility is the opposite of TypeScript's built-in Readonly<T> utility type.

Uses the -readonly modifier syntax to explicitly remove readonly modifiers from all properties at the top level of the object type.

Type Parameters

T
The object type to make mutable.

Returns

An object type with all readonly modifiers removed.

Example

type ReadonlyUser = {
  readonly id: number;
  readonly name: string;
  readonly email: string;
};

type MutableUser = Mutable<ReadonlyUser>;
// Result: { id: number; name: string; email: string }

const user: MutableUser = { id: 1, name: "Alice", email: "alice@example.com" };
user.name = "Alice Smith"; // ✓ allowed - property is mutable

// Useful for creating editable versions of readonly data
type Config = Readonly<{ host: string; port: number; ssl: boolean }>;
type EditableConfig = Mutable<Config>; // { host: string; port: number; ssl: boolean }

Type Alias Mutable<T>

Type Parameters

Returns

Example

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