Simplify code (#2491)

src/OpenTelemetry/Metrics/DropConfiguration.cs

@@ -1,35 +0,0 @@
-// <copyright file="DropConfiguration.cs" company="OpenTelemetry Authors">
-// Copyright The OpenTelemetry Authors
-//
-// Licensed under the Apache License, Version 2.0 (the "License");
-// you may not use this file except in compliance with the License.
-// You may obtain a copy of the License at
-//
-//     http://www.apache.org/licenses/LICENSE-2.0
-//
-// Unless required by applicable law or agreed to in writing, software
-// distributed under the License is distributed on an "AS IS" BASIS,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-// </copyright>
-
-using System;
-
-namespace OpenTelemetry.Metrics
-{
-    internal class DropConfiguration : MetricStreamConfiguration
-    {
-        private Aggregation aggregation = Aggregation.Drop;
-
-        public override Aggregation Aggregation
-        {
-            get => this.aggregation;
-
-            set
-            {
-                throw new ArgumentException($"Aggregation cannot be set.");
-            }
-        }
-    }
-}

src/OpenTelemetry/Metrics/MetricStreamConfiguration.cs

@@ -41,5 +41,14 @@ namespace OpenTelemetry.Metrics
         public virtual Aggregation Aggregation { get; set; }
 
         // TODO: MetricPoints caps can be configured here
+
+        private sealed class DropConfiguration : MetricStreamConfiguration
+        {
+            public override Aggregation Aggregation
+            {
+                get => Aggregation.Drop;
+                set { }
+            }
+        }
     }
 }

test/OpenTelemetry.Tests/Metrics/MetricViewTests.cs

@@ -370,7 +370,8 @@ namespace OpenTelemetry.Metrics.Tests
         [Fact]
         public void MetricStreamConfigurationForDropMustNotAllowOverriding()
         {
-            Assert.Throws<ArgumentException>(() => MetricStreamConfiguration.Drop.Aggregation = Aggregation.Histogram);
+            MetricStreamConfiguration.Drop.Aggregation = Aggregation.Histogram;
+            Assert.Equal(Aggregation.Drop, MetricStreamConfiguration.Drop.Aggregation);
         }
     }
 #pragma warning restore SA1000 // KeywordsMustBeSpacedCorrectly