type-fest/source/readonly-deep.d.ts

A collection of essential TypeScript types

import type {BuiltIns, HasMultipleCallSignatures} from './internal/index.d.ts';

/**
Convert `object`s, `Map`s, `Set`s, and `Array`s and all of their keys/elements into immutable structures recursively.

This is useful when a deeply nested structure needs to be exposed as completely immutable, for example, an imported JSON module or when receiving an API response that is passed around.

Please upvote [this issue](https://github.com/microsoft/TypeScript/issues/13923) if you want to have this type as a built-in in TypeScript.

@example
```
import type {ReadonlyDeep} from 'type-fest';

declare const foo: {
	a: string;
	b: {c: number};
	d: Array<{e: number}>;
};

foo.a = 'bar'; // Allowed

foo.b = {c: 3}; // Allowed

foo.b.c = 4; // Allowed

foo.d = [{e: 5}]; // Allowed

foo.d.push({e: 6}); // Allowed

const last = foo.d.at(-1);
if (last) {
	last.e = 7; // Allowed
}

declare const readonlyFoo: ReadonlyDeep<typeof foo>;

// @ts-expect-error
readonlyFoo.a = 'bar';
// Error: Cannot assign to 'a' because it is a read-only property.

// @ts-expect-error
readonlyFoo.b = {c: 3};
// Error: Cannot assign to 'b' because it is a read-only property.

// @ts-expect-error
readonlyFoo.b.c = 4;
// Error: Cannot assign to 'c' because it is a read-only property.

// @ts-expect-error
readonlyFoo.d = [{e: 5}];
// Error: Cannot assign to 'd' because it is a read-only property.

// @ts-expect-error
readonlyFoo.d.push({e: 6});
// Error: Property 'push' does not exist on type 'ReadonlyArray<{readonly e: number}>'.

const readonlyLast = readonlyFoo.d.at(-1);
if (readonlyLast) {
	// @ts-expect-error
	readonlyLast.e = 8;
	// Error: Cannot assign to 'e' because it is a read-only property.
}
```

Note that types containing overloaded functions are not made deeply readonly due to a [TypeScript limitation](https://github.com/microsoft/TypeScript/issues/29732).

@category Object
@category Array
@category Set
@category Map
*/
export type ReadonlyDeep<T> = T extends BuiltIns
	? T
	: T extends new (...arguments_: any[]) => unknown
		? T // Skip class constructors
		: T extends (...arguments_: any[]) => unknown
			? {} extends _ReadonlyObjectDeep<T>
				? T
				: HasMultipleCallSignatures<T> extends true
					? T
					: ((...arguments_: Parameters<T>) => ReturnType<T>) & _ReadonlyObjectDeep<T>
			: T extends Readonly<ReadonlyMap<infer KeyType, infer ValueType>>
				? ReadonlyMapDeep<KeyType, ValueType>
				: T extends Readonly<ReadonlySet<infer ItemType>>
					? ReadonlySetDeep<ItemType>
					: // Identify tuples to avoid converting them to arrays inadvertently; special case `readonly [...never[]]`, as it emerges undesirably from recursive invocations of ReadonlyDeep below.
					T extends readonly [] | readonly [...never[]]
						? readonly []
						: T extends readonly [infer U, ...infer V]
							? readonly [ReadonlyDeep<U>, ...ReadonlyDeep<V>]
							: T extends readonly [...infer U, infer V]
								? readonly [...ReadonlyDeep<U>, ReadonlyDeep<V>]
								: T extends ReadonlyArray<infer ItemType>
									? ReadonlyArray<ReadonlyDeep<ItemType>>
									: T extends object
										? _ReadonlyObjectDeep<T>
										: unknown;

/**
Same as `ReadonlyDeep`, but accepts only `ReadonlyMap`s as inputs. Internal helper for `ReadonlyDeep`.
*/
type ReadonlyMapDeep<KeyType, ValueType> = {} & Readonly<ReadonlyMap<ReadonlyDeep<KeyType>, ReadonlyDeep<ValueType>>>;

/**
Same as `ReadonlyDeep`, but accepts only `ReadonlySet`s as inputs. Internal helper for `ReadonlyDeep`.
*/
type ReadonlySetDeep<ItemType> = {} & Readonly<ReadonlySet<ReadonlyDeep<ItemType>>>;

/**
Same as `ReadonlyDeep`, but accepts only `object`s as inputs. Internal helper for `ReadonlyDeep`.
*/
export type _ReadonlyObjectDeep<ObjectType extends object> = {
	readonly [KeyType in keyof ObjectType]: ReadonlyDeep<ObjectType[KeyType]>
};

export {};