From 78b26d2d40e0da9024d5370cff5e7a94e798bc70 Mon Sep 17 00:00:00 2001
From: Jaco Greeff <jacogr@gmail.com>
Date: Sun, 31 Jan 2021 12:48:05 +0100
Subject: [PATCH] Allow .slice on Vec types (#3130)

* Allow .slice on Vec types

* Apply suggestions from code review

* Update packages/types/src/codec/AbstractArray.ts
---
 packages/types/src/codec/AbstractArray.ts |  7 +++++++
 packages/types/src/codec/Vec.spec.ts      | 10 ++++++++++
 2 files changed, 17 insertions(+)

diff --git a/packages/types/src/codec/AbstractArray.ts b/packages/types/src/codec/AbstractArray.ts
index 2660b2a9ea..56cac3c504 100644
--- a/packages/types/src/codec/AbstractArray.ts
+++ b/packages/types/src/codec/AbstractArray.ts
@@ -159,4 +159,11 @@ export abstract class AbstractArray<T extends Codec> extends Array<T> implements
   public includes (check: unknown): boolean {
     return this.some((value: T) => value.eq(check));
   }
+
+  /**
+   * @description Returns a slice of an array
+   */
+  public slice (start?: number, end?: number): T[] {
+    return this.toArray().slice(start, end);
+  }
 }
diff --git a/packages/types/src/codec/Vec.spec.ts b/packages/types/src/codec/Vec.spec.ts
index b65f8a117f..62db80ec87 100644
--- a/packages/types/src/codec/Vec.spec.ts
+++ b/packages/types/src/codec/Vec.spec.ts
@@ -6,6 +6,7 @@ import type { Codec, CodecTo } from '../types';
 
 import { Metadata } from '@polkadot/metadata';
 import rpcMetadata from '@polkadot/metadata/static';
+import { randomAsU8a } from '@polkadot/util-crypto';
 
 import { createTypeUnsafe, TypeRegistry } from '../create';
 import { GenericAccountId as AccountId } from '../generic';
@@ -170,5 +171,14 @@ describe('Vec', (): void => {
 
       expect(vec.indexOf(myId)).toEqual(2);
     });
+
+    it('allows a slice operator', (): void => {
+      const vec = registry.createType('Vec<AccountId>', [
+        randomAsU8a(), randomAsU8a(), randomAsU8a(), randomAsU8a(), randomAsU8a(), randomAsU8a(), randomAsU8a(), randomAsU8a(), randomAsU8a(), randomAsU8a()
+      ]);
+
+      expect(vec).toHaveLength(10);
+      expect(vec.slice(2, 7)).toHaveLength(5);
+    });
   });
 });