Readonly

Use ft.Readable to change an array or object Codec from mutable to readonly. It will not have any effect on the actual behaviour of the Codec, other than the results of ft.showType and the inferred TypeScript type.

The inverse is also available as ft.Mutable

Readonly Array

import * as ft from "funtypes";

const ArrayCodec = ft.Array(ft.Number);
// => Codec<number[]>

const ReadonlyArrayCodec =
  ft.Readonly(ArrayCodec);
// => Codec<readonly number[]>

type ReadonlyArray = ft.Static<
  typeof ReadonlyArrayCodec
>;
// => readonly number[]

assert.deepEqual(
  ft.showType(ReadonlyArrayCodec),
  "readonly number[]",
);

Readonly Object

import * as ft from "funtypes";

const UserCodec = ft.Object({
  id: ft.Number,
  name: ft.String,
});
// => Codec<{ id: number; name: string }>

const ReadonlyUserCodec = ft.Readonly(
  ReadonlyUserCodec,
);
// => Codec<{ readonly id: number; readonly name: string }>

type ReadonlyUser = ft.Static<
  typeof ReadonlyUserCodec
>;
// => { readonly id: number; readonly name: string }

assert.deepEqual(
  ft.showType(ReadonlyUserCodec),
  "{ readonly id: number; readonly name: string }",
);

Readonly Tuple

import * as ft from "funtypes";

const TupleCodec = ft.Tuple(ft.Number, ft.String);
// => Codec<[ number, string ]>

const ReadonlyTupleCodec =
  ft.Readonly(TupleCodec);
// => Codec<readonly [ number, string ]>

type ReadonlyTuple = ft.Static<
  typeof ReadonlyTupleCodec
>;
// => readonly [ number, string ]

assert.deepEqual(
  ft.showType(ReadonlyTupleCodec),
  "readonly [ number, string ]",
);

Make everything readonly

If you prefer to use Readonly for most things, you can import from "funtypes/readonly" instead of "funtypes" and it will swap the default so that ft.Array, ft.Object, ft.Record and ft.Tuple would be readonly and you'd need to do ft.MutableArray, ft.MutableObject, ft.MutableRecord and ft.MutableTuple for the mutable versions.

import * as ft from "funtypes/readonly";

export const MyArrayCodec = ft.Array(ft.Number);
// => ft.Codec<readonly number[]>

export const MyMutableArrayCodec =
  ft.MutableArray(ft.Number);
// => ft.Codec<number[]>