Implement Keys and Values as views

csharp/src/Google.Protobuf.Test/Collections/MapFieldTest.cs

@@ -477,6 +477,77 @@ namespace Google.Protobuf.Collections
             Assert.IsTrue(new MapField<int, int?>(true).AllowsNullValues);
         }
 
+        [Test]
+        public void KeysReturnsLiveView()
+        {
+            var map = new MapField<string, string>();
+            var keys = map.Keys;
+            CollectionAssert.AreEqual(new string[0], keys);
+            map["foo"] = "bar";
+            map["x"] = "y";
+            CollectionAssert.AreEqual(new[] { "foo", "x" }, keys);
+        }
+
+        [Test]
+        public void ValuesReturnsLiveView()
+        {
+            var map = new MapField<string, string>();
+            var values = map.Values;
+            CollectionAssert.AreEqual(new string[0], values);
+            map["foo"] = "bar";
+            map["x"] = "y";
+            CollectionAssert.AreEqual(new[] { "bar", "y" }, values);
+        }
+
+        // Just test keys - we know the implementation is the same for values
+        [Test]
+        public void ViewsAreReadOnly()
+        {
+            var map = new MapField<string, string>();
+            var keys = map.Keys;
+            Assert.IsTrue(keys.IsReadOnly);
+            Assert.Throws<NotSupportedException>(() => keys.Clear());
+            Assert.Throws<NotSupportedException>(() => keys.Remove("a"));
+            Assert.Throws<NotSupportedException>(() => keys.Add("a"));
+        }
+
+        // Just test keys - we know the implementation is the same for values
+        [Test]
+        public void ViewCopyTo()
+        {
+            var map = new MapField<string, string> { { "foo", "bar" }, { "x", "y" } };
+            var keys = map.Keys;
+            var array = new string[4];
+            Assert.Throws<ArgumentException>(() => keys.CopyTo(array, 3));
+            Assert.Throws<ArgumentOutOfRangeException>(() => keys.CopyTo(array, -1));
+            keys.CopyTo(array, 1);
+            CollectionAssert.AreEqual(new[] { null, "foo", "x", null }, array);
+        }
+
+        [Test]
+        public void KeysContains()
+        {
+            var map = new MapField<string, string> { { "foo", "bar" }, { "x", "y" } };
+            var keys = map.Keys;
+            Assert.IsTrue(keys.Contains("foo"));
+            Assert.IsFalse(keys.Contains("bar")); // It's a value!
+            Assert.IsFalse(keys.Contains("1"));
+            // Keys can't be null, so we should prevent contains check
+            Assert.Throws<ArgumentNullException>(() => keys.Contains(null));
+        }
+
+        [Test]
+        public void ValuesContains()
+        {
+            var map = new MapField<string, string> { { "foo", "bar" }, { "x", "y" } };
+            var values = map.Values;
+            Assert.IsTrue(values.Contains("bar"));
+            Assert.IsFalse(values.Contains("foo")); // It's a key!
+            Assert.IsFalse(values.Contains("1"));
+            // Values can be null, so this makes sense
+            Assert.IsFalse(values.Contains(null));
+        }
+
         private static KeyValuePair<TKey, TValue> NewKeyValuePair<TKey, TValue>(TKey key, TValue value)
         {
             return new KeyValuePair<TKey, TValue>(key, value);

csharp/src/Google.Protobuf/Collections/MapField.cs

@@ -136,6 +136,12 @@ namespace Google.Protobuf.Collections
             return map.ContainsKey(key);
         }
 
+        private bool ContainsValue(TValue value)
+        {
+            var comparer = EqualityComparer<TValue>.Default;
+            return list.Any(pair => comparer.Equals(pair.Value, value));
+        }
+
         /// <summary>
         /// Removes the entry identified by the given key from the map.
         /// </summary>
@@ -221,17 +227,15 @@ namespace Google.Protobuf.Collections
             }
         }
 
-        // TODO: Make these views?
-
         /// <summary>
         /// Gets a collection containing the keys in the map.
         /// </summary>
-        public ICollection<TKey> Keys { get { return list.Select(t => t.Key).ToList(); } }
+        public ICollection<TKey> Keys { get { return new MapView<TKey>(this, pair => pair.Key, ContainsKey); } }
 
         /// <summary>
         /// Gets a collection containing the values in the map.
         /// </summary>
-        public ICollection<TValue> Values { get { return list.Select(t => t.Value).ToList(); } }
+        public ICollection<TValue> Values { get { return new MapView<TValue>(this, pair => pair.Value, ContainsValue); } }
 
         /// <summary>
         /// Adds the specified entries to the map.
@@ -658,5 +662,81 @@ namespace Google.Protobuf.Collections
                 MessageDescriptor IMessage.Descriptor { get { return null; } }
             }
         }
+
+        private class MapView<T> : ICollection<T>, ICollection
+        {
+            private readonly MapField<TKey, TValue> parent;
+            private readonly Func<KeyValuePair<TKey, TValue>, T> projection;
+            private readonly Func<T, bool> containsCheck;
+
+            internal MapView(
+                MapField<TKey, TValue> parent,
+                Func<KeyValuePair<TKey, TValue>, T> projection,
+                Func<T, bool> containsCheck)
+            {
+                this.parent = parent;
+                this.projection = projection;
+                this.containsCheck = containsCheck;
+            }
+
+            public int Count { get { return parent.Count; } }
+
+            public bool IsReadOnly { get { return true; } }
+
+            public bool IsSynchronized { get { return false; } }
+
+            public object SyncRoot { get { return parent; } }
+
+            public void Add(T item)
+            {
+                throw new NotSupportedException();
+            }
+
+            public void Clear()
+            {
+                throw new NotSupportedException();
+            }
+
+            public bool Contains(T item)
+            {
+                return containsCheck(item);
+            }
+
+            public void CopyTo(T[] array, int arrayIndex)
+            {
+                if (arrayIndex < 0)
+                {
+                    throw new ArgumentOutOfRangeException("arrayIndex");
+                }
+                if (arrayIndex + Count  >= array.Length)
+                {
+                    throw new ArgumentException("Not enough space in the array", "array");
+                }
+                foreach (var item in this)
+                {
+                    array[arrayIndex++] = item;
+                }
+            }
+
+            public IEnumerator<T> GetEnumerator()
+            {
+                return parent.list.Select(projection).GetEnumerator();
+            }
+
+            public bool Remove(T item)
+            {
+                throw new NotSupportedException();
+            }
+
+            IEnumerator IEnumerable.GetEnumerator()
+            {
+                return GetEnumerator();
+            }
+
+            public void CopyTo(Array array, int index)
+            {
+                throw new NotImplementedException();
+            }
+        }
     }
 }