feat(ensurePromise): add ensurePromise function

Author: lambdalisue

deno.jsonc

@@ -5,6 +5,7 @@
     ".": "./mod.ts",
     "./async-value": "./async_value.ts",
     "./barrier": "./barrier.ts",
+    "./ensure-promise": "./ensure_promise.ts",
     "./lock": "./lock.ts",
     "./mutex": "./mutex.ts",
     "./notify": "./notify.ts",
@@ -34,6 +35,7 @@
     "@core/asyncutil": "./mod.ts",
     "@core/asyncutil/async-value": "./async_value.ts",
     "@core/asyncutil/barrier": "./barrier.ts",
+    "@core/asyncutil/ensure-promise": "./ensure_promise.ts",
     "@core/asyncutil/lock": "./lock.ts",
     "@core/asyncutil/mutex": "./mutex.ts",
     "@core/asyncutil/notify": "./notify.ts",

ensure_promise.ts

@@ -0,0 +1,20 @@
+/**
+ * Ensure that a value is a promise.
+ *
+ * It returns the value if it is already a promise, otherwise it returns a
+ * promise that resolves to the value.
+ *
+ * @param value - The value to ensure as a promise.
+ * @returns A promise that resolves to the value.
+ *
+ * ```ts
+ * import { assertEquals } from "@std/assert";
+ * import { ensurePromise } from "@core/asyncutil/ensure-promise";
+ *
+ * assertEquals(await ensurePromise(42), 42);
+ * assertEquals(await ensurePromise(Promise.resolve(42)), 42);
+ * ```
+ */
+export function ensurePromise<T>(value: T): Promise<T> {
+  return value instanceof Promise ? value : Promise.resolve(value);
+}

ensure_promise_test.ts

@@ -0,0 +1,12 @@
+import { test } from "@cross/test";
+import { assertEquals } from "@std/assert";
+import { ensurePromise } from "./ensure_promise.ts";
+
+test("ensurePromise() returns the value if it is already a promise", async () => {
+  const p = Promise.resolve(42);
+  assertEquals(await ensurePromise(p), 42);
+});
+
+test("ensurePromise() returns a promise that resolves to the value", async () => {
+  assertEquals(await ensurePromise(42), 42);
+});