add ascending to IterableExtension.sortedBy

Author: arthurbcd

pkgs/collection/lib/src/iterable_extensions.dart

@@ -6,7 +6,6 @@ import 'dart:math' show Random;
 
 import 'algorithms.dart';
 import 'functions.dart' as functions;
-import 'utils.dart';
 
 /// Extensions that apply to all iterables.
 ///
@@ -71,10 +70,15 @@ extension IterableExtension<T> on Iterable<T> {
   /// Creates a sorted list of the elements of the iterable.
   ///
   /// The elements are ordered by the natural ordering of the
-  /// property [keyOf] of the element.
-  List<T> sortedBy<K extends Comparable<K>>(K Function(T element) keyOf) {
+  /// [keyOf] property when [ascending] is `true` or reverse ordering
+  /// when [ascending] is `false`.
+  List<T> sortedBy<K extends Comparable<K>>(
+    K Function(T element) keyOf, {
+    bool ascending = true,
+  }) {
+    int compare(K a, K b) => ascending ? a.compareTo(b) : b.compareTo(a);
     var elements = [...this];
-    mergeSortBy<T, K>(elements, keyOf, compareComparable);
+    mergeSortBy<T, K>(elements, keyOf, compare);
     return elements;
   }
 

pkgs/collection/test/extensions_test.dart

@@ -64,6 +64,16 @@ void main() {
         test('multiple', () {
           expect(iterable(<int>[3, 20, 100]).sortedBy(toString), [100, 20, 3]);
         });
+        test('multiple ascending', () {
+          expect(
+              iterable(<int>[3, 20, 100]).sortedBy(toString, ascending: true),
+              [100, 20, 3]);
+        });
+        test('multiple descending', () {
+          expect(
+              iterable(<int>[3, 20, 100]).sortedBy(toString, ascending: false),
+              [3, 20, 100]);
+        });
       });
       group('.sortedByCompare', () {
         test('empty', () {