# System.Runtime.CompilerServices

``` diff
 namespace System.Runtime.CompilerServices {
+    public sealed class CompilerFeatureRequiredAttribute : Attribute {
+        public const string RefStructs = "RefStructs";
+        public const string RequiredMembers = "RequiredMembers";
+        public CompilerFeatureRequiredAttribute(string featureName);
+        public string FeatureName { get; }
+        public bool IsOptional { get; set; }
+    }
     public sealed class ConditionalWeakTable<TKey, TValue> : IEnumerable, IEnumerable<KeyValuePair<TKey, TValue>> where TKey : class where TValue : class? {
+        public bool TryAdd(TKey key, TValue value);
     }
 }
```

