feat(typescript-types): Add IsUnknown<T>

packages/typescript-types/README.md

@@ -25,6 +25,7 @@ The types included in this library are categorized by their purpose.
 | [`IsAny<T>`][]                          | `true` if `T` is `any`, `false` otherwise (`null`, `undefined` also yield `false`)                        |
 | [`IsNever<T>`][]                        | `true` if `T` is `never`, `false` otherwise (`null`, `undefined`, `any` also yield `false`)               |
 | [`IsUndefined<T>`][]                    | `true` if `T` is `undefined`, `false` otherwise (`null`, `never`, `any` also yield `false`).              |
+| [`IsUnknown<T>`][]                      | `true` if `T` is `unknown`, `false` otherwise (`null`, `never`, `any` also yield `false`).                |
 | [`If<Test, TrueBranch, FalseBranch>`][] | Returns `TrueBranch` if `Test` is `true`, `FalseBranch` otherwise[^if_remark].                            |
 | [`IsKeyOf<T, K>`][]                     | `true` if `K` is a key of `T`, `false` otherwise. If `T` is `any`, any `K` but `never` will yield `true`. |
 | [`IsEmptyString<S>`][]                  | `true` if `S` is the empty string `''`, `false` otherwise.[^is-empty-string_remark]                       |
@@ -36,6 +37,7 @@ The types included in this library are categorized by their purpose.
 [`IsAny<T>`]: src/is-any.ts
 [`IsNever<T>`]: src/is-never.ts
 [`IsUndefined<T>`]: src/is-undefined.ts
+[`IsUnknown<T>`]: src/is-unknown.ts
 [`If<Test, TrueBranch, FalseBranch>`]: src/if.ts
 [`IsKeyOf<T, K>`]: src/is-key-of.ts
 [`IsEmptyString<S>`]: src/is-empty-string.ts

packages/typescript-types/src/is-unknown.ts

@@ -0,0 +1,9 @@
+import type { If } from './if.js'
+import type { IsAny } from './is-any.js'
+import type { IsNever } from './is-never.js'
+
+export type IsUnknown<T> = If<
+	IsAny<T>,
+	false,
+	If<IsNever<T>, false, T extends unknown ? (unknown extends T ? true : false) : false>
+>

packages/typescript-types/test/is-unknown.tst.ts

@@ -0,0 +1,11 @@
+import type { IsUnknown } from '@/is-unknown.js'
+import { expect } from 'tstyche'
+
+expect<IsUnknown<unknown>>().type.toBe<true>()
+
+expect<IsUnknown<1>>().type.toBe<false>()
+expect<IsUnknown<'somestring'>>().type.toBe<false>()
+expect<IsUnknown<null>>().type.toBe<false>()
+expect<IsUnknown<undefined>>().type.toBe<false>()
+expect<IsUnknown<any>>().type.toBe<false>()
+expect<IsUnknown<never>>().type.toBe<false>()