Tweaks

Author: rolfbjarne

src/Foundation/NSMutableDictionary_2.cs

@@ -237,13 +237,11 @@ public bool ContainsKey (TKey key)
 		/// Gets or sets the value associated with the specified key.
 		/// </summary>
 		/// <param name="index">The key of the value to get or set.</param>
-		/// <returns>The value associated with the specified key.</returns>
-		public TValue this [TKey index] {
+		/// <returns>The value associated with the specified key, or <see langword="null" /> if the key wasn't found.</returns>
+		[DisallowNull] // don't allow setting null values
+		public TValue? this [TKey index] {
 			get {
-				var result = ObjectForKey (index);
-				if (result is null)
-					throw new KeyNotFoundException ();
-				return result;
+				return ObjectForKey (index);
 			}
 			set {
 				Add (index, value);
@@ -368,15 +366,16 @@ bool IDictionary<TKey, TValue>.Remove (TKey key)
 			return Remove (key);
 		}
 
-		bool IDictionary<TKey, TValue>.TryGetValue (TKey key, [MaybeNullWhen (false)] out TValue value)
+		bool IDictionary<TKey, TValue>.TryGetValue (TKey key, [NotNullWhen (true)]  out TValue? value)
 		{
-			var result = TryGetValue (key, out var nullableValue);
-			value = nullableValue!;
-			return result;
+			return TryGetValue (key, out value);
 		}
 
-		TValue IDictionary<TKey, TValue>.this [TKey index] {
+		[DisallowNull] // don't allow setting null values
+		TValue? IDictionary<TKey, TValue>.this [TKey index] {
+#pragma warning disable CS8768 // Nullability of reference types in return type doesn't match implemented member 'TValue IDictionary<TKey, TValue>.this[TKey key].get'
 			get {
+#pragma warning restore CS8768
 				return this [index];
 			}
 			set {

tests/monotouch-test/Foundation/NSMutableDictionary2Test.cs

@@ -358,18 +358,18 @@ public void IndexerTest ()
 		}
 
 		[Test]
-		public void IndexerGetterThrowsKeyNotFoundTest ()
+		public void IndexerGetterKeyNotFoundBehaviorTest ()
 		{
 			var value1 = NSDate.FromTimeIntervalSinceNow (1);
 			var key1 = new NSString ("key1");
 			var keyMissing = new NSString ("missing");
 
 			var dict = new NSMutableDictionary<NSString, NSDate> (key1, value1);
 
-			// Accessing via the indexer property should throw KeyNotFoundException for missing keys
-			Assert.Throws<KeyNotFoundException> (() => GC.KeepAlive (dict [keyMissing]), "missing key");
+			// Accessing via the indexer property should return null
+			Assert.IsNull (dict [keyMissing], "missing key");
 
-			// But accessing via IDictionary interface should return null
+			// Accessing via IDictionary interface should return null too
 			IDictionary<NSString, NSDate> idict = dict;
 			Assert.IsNull (idict [keyMissing], "missing key via interface");
 		}
@@ -399,10 +399,10 @@ public void MissingKeyAccessTest ()
 			// ContainsKey should return false for missing keys
 			Assert.IsFalse (dict.ContainsKey (keyMissing), "ContainsKey missing");
 
-			// Indexer getter should throw KeyNotFoundException
-			Assert.Throws<KeyNotFoundException> (() => GC.KeepAlive (dict [keyMissing]), "Indexer missing");
+			// Indexer getter should return null
+			Assert.IsNull (dict [keyMissing], "Indexer missing");
 
-			// But IDictionary indexer should return null
+			// IDictionary indexer should also return null
 			IDictionary<NSString, NSDate> idict = dict;
 			Assert.IsNull (idict [keyMissing], "IDictionary indexer missing");
 		}
@@ -421,7 +421,7 @@ public void EmptyDictionaryMissingKeyTest ()
 			Assert.IsFalse (dict.TryGetValue (keyMissing, out value), "TryGetValue");
 			Assert.IsNull (value, "TryGetValue out");
 
-			Assert.Throws<KeyNotFoundException> (() => GC.KeepAlive (dict [keyMissing]), "Indexer");
+			Assert.IsNull (dict [keyMissing], "Indexer");
 
 			IDictionary<NSString, NSDate> idict = dict;
 			Assert.IsNull (idict [keyMissing], "IDictionary indexer");