feat: add PromiseOr utility

src/types/utils.ts

@@ -32,3 +32,10 @@ export declare class Tagged<N extends string> { private _nominal_: N; }
  * @returns a type that is equal only to itself, but can be used like its contained type `T`
  */
 export type Nominal<T, N extends string> = T & Tagged<N>;
+
+/**
+ * Returns the given type or a Promise containing that type.
+ * @param T the inner type for the promise
+ * @returns a the type union with a promise containing the given type
+ */
+export type PromiseOr<T> = Promise<T> | T;

test/utils/PromiseOr.test.ts

@@ -0,0 +1,11 @@
+import test from 'ava';
+import { assert } from '../helpers/assert';
+
+import { PromiseOr } from '../../src';
+
+test('Will give back a promise containing given type union the type itself', t => {
+    type got = PromiseOr<string>;
+    type expected = Promise<string> | string;
+
+    assert<got, expected>(t);
+});