feat: add concurrent function to slice

src/Lazy/slice.ts

@@ -1,6 +1,7 @@
 import isNumber from "../isNumber";
 import ReturnIterableIteratorType from "../types/ReturnIterableIteratorType";
 import { isAsyncIterable, isIterable } from "../_internal/utils";
+import concurrent, { isConcurrent } from "./concurrent";
 
 function* sync<T>(
   start = 0,
@@ -16,7 +17,7 @@ function* sync<T>(
   }
 }
 
-async function* async<T>(
+async function* asyncSequential<T>(
   start = 0,
   end = Infinity,
   iterable: AsyncIterable<T>,
@@ -30,6 +31,30 @@ async function* async<T>(
   }
 }
 
+function async<T>(
+  start = 0,
+  end = Infinity,
+  iterable: AsyncIterable<T>,
+): AsyncIterableIterator<T> {
+  let iterator: AsyncIterator<T>;
+  return {
+    [Symbol.asyncIterator]() {
+      return this;
+    },
+
+    async next(_concurrent: any) {
+      if (iterator === undefined) {
+        // prettier-ignore
+        iterator = isConcurrent(_concurrent)
+          ? asyncSequential(start, end, concurrent(_concurrent.length, iterable))
+          : asyncSequential(start, end, iterable);
+      }
+
+      return iterator.next(_concurrent);
+    },
+  };
+}
+
 function _slice<T extends Iterable<unknown> | AsyncIterable<unknown>>(
   start: number,
   end: number,

test/Lazy/slice.spec.ts

@@ -1,4 +1,6 @@
 import { pipe, slice, toArray, toAsync } from "../../src";
+import { Concurrent } from "../../src/Lazy/concurrent";
+import { generatorMock } from "../utils";
 
 describe("slice", function () {
   describe("sync", function () {
@@ -81,5 +83,13 @@ describe("slice", function () {
       const res2 = await pipe([1, 2, 3, 4, 5], toAsync, slice(1, 3), toArray);
       expect(res2).toEqual([2, 3]);
     });
+
+    it("should be passed concurrent object when job works concurrently", async function () {
+      const mock = generatorMock();
+      const iter = slice(1, 2, mock);
+      const concurrent = Concurrent.of(2) as any;
+      await iter.next(concurrent);
+      expect((mock as any).getConcurrent()).toEqual(concurrent);
+    });
   });
 });