Merge pull request #76 from passsy/feature/take_last_while

KtList.takeLastWhile(predicate)
passsy · Feb 16, 2019 · 06da362 · 06da362
2 parents 5a051db + 2667e92
commit 06da362
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Showing 4 changed files with 68 additions and 1 deletion.
diff --git a/lib/src/collection/extension/list_extension_mixin.dart b/lib/src/collection/extension/list_extension_mixin.dart
@@ -263,4 +263,27 @@ abstract class KtListExtensionsMixin<T>
     }
     return list;
   }
+
+  @override
+  KtList<T> takeLastWhile(bool Function(T) predicate) {
+    assert(() {
+      if (predicate == null) throw ArgumentError("predicate can't be null");
+      return true;
+    }());
+    if (isEmpty()) return emptyList();
+    final iterator = listIterator(size);
+    while (iterator.hasPrevious()) {
+      if (!predicate(iterator.previous())) {
+        iterator.next();
+        final expectedSize = size - iterator.nextIndex();
+        if (expectedSize == 0) return emptyList();
+        final list = mutableListOf<T>();
+        while (iterator.hasNext()) {
+          list.add(iterator.next());
+        }
+        return list;
+      }
+    }
+    return toList();
+  }
 }
diff --git a/lib/src/collection/kt_list.dart b/lib/src/collection/kt_list.dart
@@ -207,4 +207,9 @@ abstract class KtListExtension<T> {
    * Returns a list containing last [n] elements.
    */
   KtList<T> takeLast(int n);
+
+  /**
+   * Returns a list containing last elements satisfying the given [predicate].
+   */
+  KtList<T> takeLastWhile(bool Function(T) predicate);
 }
diff --git a/test/collection/iterable_extensions_test.dart b/test/collection/iterable_extensions_test.dart
@@ -73,7 +73,7 @@ void testIterable(KtIterable<T> Function<T>() emptyIterable,
     test("predicate can't be null", () {
       final iterable = iterableOf(["abc", "bcd", "cde"]);
       final e = catchException<ArgumentError>(() => iterable.all(null));
-      expect(e.message, allOf(contains("null")));
+      expect(e.message, allOf(contains("predicate"), contains("null")));
     });
   });
 

diff --git a/test/collection/list_extensions_test.dart b/test/collection/list_extensions_test.dart
@@ -302,4 +302,43 @@ void testList(
       expect(list.takeLast(2).toList(), listFrom([1, null]));
     });
   });
+
+  group("takeLastWhile", () {
+    test("take no elements returns empty", () {
+      final list = listOf(1, 2, 3, 4);
+      expect(list.takeLastWhile((it) => false), emptyList());
+    });
+
+    test("take all elements returns original list", () {
+      final list = listOf(1, 2, 3, 4);
+      expect(list.takeLastWhile((it) => true), list.toList());
+    });
+
+    if (ordered) {
+      test("takeLastWhile larger 2", () {
+        final list = listOf(1, 2, 3, 4);
+        expect(list.takeLastWhile((it) => it > 2), listOf(3, 4));
+      });
+    }
+
+    if (ordered) {
+      test("takeLastWhile larger 1", () {
+        final list = listOf(1, 2, 3, 4);
+        expect(list.takeLastWhile((it) => it > 1), listOf(2, 3, 4));
+      });
+    }
+
+    if (ordered) {
+      test("takeLastWhile larger 3", () {
+        final list = listOf(1, 2, 3, 4);
+        expect(list.takeLastWhile((it) => it > 3), listOf(4));
+      });
+    }
+
+    test("predicate can't be null", () {
+      final list = listOf("a", "b", "c");
+      final e = catchException<ArgumentError>(() => list.takeLastWhile(null));
+      expect(e.message, allOf(contains("null"), contains("predicate")));
+    });
+  });
 }