feat(types): Fn

Signed-off-by: Lexus Drumgold <[email protected]>

src/types/__tests__/fn.spec-d.ts

@@ -0,0 +1,19 @@
+/**
+ * @file Type Tests - Fn
+ * @module tutils/types/tests/unit-d/Fn
+ */
+
+import type ANY from '../any'
+import type TestSubject from '../fn'
+
+describe('unit-d:types/Fn', () => {
+  it('should be callable with Args', () => {
+    expectTypeOf<TestSubject>().parameters.toEqualTypeOf<ANY[]>()
+    expectTypeOf<TestSubject<[string]>>().parameters.toEqualTypeOf<[string]>()
+  })
+
+  it('should return Ret', () => {
+    expectTypeOf<TestSubject>().returns.toEqualTypeOf<ANY>()
+    expectTypeOf<TestSubject<ANY, string>>().returns.toBeString()
+  })
+})

src/types/fn.ts

@@ -0,0 +1,18 @@
+/**
+ * @file Type Definitions - Fn
+ * @module tutils/types/Fn
+ */
+
+import type ANY from './any'
+
+/**
+ * A function.
+ *
+ * @template Args - Arguments type
+ * @template Ret - Return type
+ */
+type Fn<Args extends ANY[] = ANY[], Ret extends ANY = ANY> = (
+  ...args: Args
+) => Ret
+
+export type { Fn as default }

src/types/index.ts

@@ -17,6 +17,7 @@ export type {
   default as ExactOptionalPropertyTypes
 } from './exact-optional-property-types'
 export type { default as FIXME } from './fixme'
+export type { default as Fn } from './fn'
 export type { default as IndexSignature } from './index-signature'
 export type { default as IsTuple } from './is-tuple'
 export type { default as Join } from './join'