feat: add readonly/readonlyArray

Author: jedwards1211

README.md

@@ -313,6 +313,11 @@ A validator that requires the value to be `string | null | undefined`.
 
 A validator that requires the value to be `number[]`.
 
+### `t.readonlyArray(t.number())`
+
+A validator that requires the value to be `number[]`.
+Doesn't require the value to be frozen; just allows the extracted type to be `ReadonlyArray`.
+
 ### `t.object(properties)`
 
 A validator that requires the value to be an object with all of the given required properties an no additional properties.
@@ -354,6 +359,10 @@ PersonType.assert({ name: 1 }) // error
 PersonType.assert({ name: 'dude', age: 'old' }) // error
 ```
 
+### `t.readonly(objectType)`
+
+Use `t.readOnly(t.object(...))` or `t.readOnly(t.merge(...))` etc. Doesn't require the object to be frozen, just allows the extracted type to be readonly.
+
 ### `t.merge(...objectTypes)`
 
 Merges the properties of multiple object validators together into an exact object validator (no additional properties are allowed).

src/index.js.flow

@@ -68,6 +68,11 @@ declare export function any(): Type<any>
 declare export function unknown(): Type<mixed>
 
 declare export function array<T>(elementType: Type<T>): Type<T[]>
+declare export function readonlyArray<T>(
+  elementType: Type<T>
+): Type<$ReadOnlyArray<T>>
+
+declare export function readonly<T: {}>(type: Type<T>): Type<$ReadOnly<T>>
 
 declare export function nullLiteral(): Type<null>
 export { nullLiteral as null }

src/index.ts

@@ -68,6 +68,12 @@ export const unknown = (): Type<unknown> => new UnknownType()
 export const array = <T>(elementType: Type<T>): Type<T[]> =>
   new ArrayType(elementType)
 
+export const readonlyArray = <T>(elementType: Type<T>): Type<readonly T[]> =>
+  new ArrayType(elementType) as any
+
+export const readonly = <T extends {}>(type: Type<T>): Type<Readonly<T>> =>
+  type as any
+
 export const nullLiteral = (): Type<null> => new NullLiteralType()
 export { nullLiteral as null }
 export const nullOr = <T>(type: Type<T>): Type<T | null> =>

test/readonly.spec.js.flow

@@ -0,0 +1,17 @@
+// @flow
+
+/* eslint-disable @typescript-eslint/no-unused-vars */
+
+import * as t from '../src/index'
+import { describe, it } from 'mocha'
+
+describe('readonly', () => {
+  type Person = $ReadOnly<{|
+    name: string,
+  |}>
+
+  const PersonType: t.TypeAlias<Person> = t.alias(
+    'Person',
+    t.readonly(t.object({ name: t.string() }))
+  )
+})

test/readonlyArray.spec.js.flow

@@ -0,0 +1,15 @@
+// @flow
+
+/* eslint-disable @typescript-eslint/no-unused-vars */
+
+import * as t from '../src/index'
+import { describe, it } from 'mocha'
+
+describe('readonlyArray', () => {
+  type Nums = $ReadOnlyArray<number>
+
+  const PersonType: t.TypeAlias<Nums> = t.alias(
+    'Person',
+    t.readonlyArray(t.number())
+  )
+})