Optimization of flatten 0 case (#1621)

* Optimizationf or flatten 0 case

* Remove wayward .123deno

CHANGELOG.md

@@ -1,5 +1,13 @@
 # CHANGELOG
 
+## master
+
+Changes:
+
+- Optimization for empty `arrayFlatten` case
+- Coding cleanups for logger (no `as` casting)
+
+
 ## 10.1.2 Jul 29, 2022
 
 Changes:

packages/util/src/array/flatten.spec.ts

@@ -1,12 +1,31 @@
 // Copyright 2017-2022 @polkadot/util authors & contributors
 // SPDX-License-Identifier: Apache-2.0
 
+import { perf } from '../test/performance';
 import { arrayFlatten } from '.';
 
+const PERF_ONE = [[1, 2, 3, 4, 5]];
+const PERF_MUL = [[1, 2, 3], [4, 5, 6], [7, 8, 9]];
+
 describe('arrayFlatten', (): void => {
   it('flattens arrays', (): void => {
     expect(
       arrayFlatten([[0], [1, 2, 3], [4, 5], [6], [], [7, 8]])
     ).toEqual([0, 1, 2, 3, 4, 5, 6, 7, 8]);
   });
+
+  it('flattens a single entry', (): void => {
+    expect(
+      arrayFlatten([[1, 2, 3, 4, 5]])
+    ).toEqual([1, 2, 3, 4, 5]);
+  });
+
+  it('flattens an empty', (): void => {
+    expect(
+      arrayFlatten([])
+    ).toEqual([]);
+  });
+
+  perf('arrayFlatten (single)', 10_000_000, [[PERF_ONE]], arrayFlatten);
+  perf('arrayFlatten (multi)', 700_000, [[PERF_MUL]], arrayFlatten);
 });

packages/util/src/array/flatten.ts

@@ -19,8 +19,10 @@
  * ```
  */
 export function arrayFlatten <T> (arrays: readonly T[][]): T[] {
-  // noop for the single-entry case
-  if (arrays.length === 1) {
+  // noop for the empty & single-entry case
+  if (arrays.length === 0) {
+    return [];
+  } else if (arrays.length === 1) {
     return arrays[0];
   }