fix: allow falsy values and null in Queue and Stack

queue.ts

@@ -17,7 +17,7 @@ import { Notify } from "./notify.ts";
  * assertEquals(await queue.pop(), 3);
  * ```
  */
-export class Queue<T> {
+export class Queue<T extends NonNullable<unknown> | null> {
   #notify = new Notify();
   #items: T[] = [];
 
@@ -52,7 +52,7 @@ export class Queue<T> {
     while (true) {
       signal?.throwIfAborted();
       const value = this.#items.shift();
-      if (value) {
+      if (value !== undefined) {
         return value;
       }
       await this.#notify.notified({ signal });

queue_test.ts

@@ -57,3 +57,21 @@ test("Queue 'pop' with signal already aborted", async () => {
     "Aborted",
   );
 });
+
+test("Queue with falsy value is accepted", async () => {
+  const q = new Queue<number>();
+  const popper = q.pop();
+  assertEquals(await promiseState(popper), "pending");
+  q.push(0);
+  assertEquals(await promiseState(popper), "fulfilled");
+  assertEquals(await popper, 0);
+});
+
+test("Queue with null is accepted", async () => {
+  const q = new Queue<null>();
+  const popper = q.pop();
+  assertEquals(await promiseState(popper), "pending");
+  q.push(null);
+  assertEquals(await promiseState(popper), "fulfilled");
+  assertEquals(await popper, null);
+});

stack.ts

@@ -19,7 +19,7 @@ import { Notify } from "./notify.ts";
  *
  * @template T The type of items in the stack.
  */
-export class Stack<T> {
+export class Stack<T extends NonNullable<unknown> | null> {
   #notify = new Notify();
   #items: T[] = [];
 
@@ -56,7 +56,7 @@ export class Stack<T> {
     while (true) {
       signal?.throwIfAborted();
       const value = this.#items.pop();
-      if (value) {
+      if (value !== undefined) {
         return value;
       }
       await this.#notify.notified({ signal });

stack_test.ts

@@ -57,3 +57,21 @@ test("Stack 'pop' with signal already aborted", async () => {
     "Aborted",
   );
 });
+
+test("Stack with falsy value is accepted", async () => {
+  const q = new Stack<number>();
+  const popper = q.pop();
+  assertEquals(await promiseState(popper), "pending");
+  q.push(0);
+  assertEquals(await promiseState(popper), "fulfilled");
+  assertEquals(await popper, 0);
+});
+
+test("Stack with null is accepted", async () => {
+  const q = new Stack<null>();
+  const popper = q.pop();
+  assertEquals(await promiseState(popper), "pending");
+  q.push(null);
+  assertEquals(await promiseState(popper), "fulfilled");
+  assertEquals(await popper, null);
+});