feat(slice): add slice function

Author: djcsdy

index.test.ts

@@ -45,6 +45,7 @@ import {
     removeFirst,
     scan,
     scan1,
+    slice,
     sum,
     tail,
     take,
@@ -99,6 +100,14 @@ test("notEmpty", async t => {
     t.is(await notEmpty(asyncIterable([1, 2, 3])), true);
 });
 
+test("slice", async t => {
+    t.deepEqual(await toArray(slice(asyncIterable([1, 2, 3, 4]), 1)), [2, 3, 4]);
+    t.deepEqual(await toArray(slice(asyncIterable([1, 2, 3, 4, 5]), 1, 4)), [2, 3, 4]);
+    t.deepEqual(await toArray(slice(asyncIterable([1, 2, 3]), 2)), [3]);
+    t.deepEqual(await toArray(slice(asyncIterable([1, 2, 3]), 0, 2)), [1, 2]);
+    t.deepEqual(await toArray(slice(asyncIterable([]), 3, 5)), []);
+});
+
 test("take", async t => {
     t.deepEqual(await toArray(take(asyncIterable([]), 3)), []);
     t.deepEqual(await toArray(take(asyncIterable([1, 2]), 3)), [1, 2]);

index.ts

@@ -156,6 +156,31 @@ export async function notEmpty(iterable: AsyncIterableLike<unknown>): Promise<bo
 
 export const asyncNotEmpty = notEmpty;
 
+export async function* slice<T>(
+    iterable: AsyncIterableLike<T>,
+    start: number | Promise<number> = 0,
+    end: number | Promise<number> = Infinity
+): AsyncIterable<T> {
+    const s = await start;
+    const e = await end;
+
+    if (e === s) {
+        return;
+    }
+
+    const iterator = asyncIterator(iterable);
+    let element = await iterator.next();
+
+    for (let i = 0; i < s && element.done !== true; ++i) {
+        element = await iterator.next();
+    }
+
+    for (let i = s; i < e && element.done !== true; ++i) {
+        yield element.value;
+        element = await iterator.next();
+    }
+}
+
 export async function* take<T>(
     iterable: AsyncIterableLike<T>,
     count: number | Promise<number>