dotnet-core/release-notes/2.1/Preview/api-diff/preview2/2.1-preview2_System.Collections.Generic.md

System.Collections.Generic

 namespace System.Collections.Generic {
     public class Dictionary<TKey, TValue> : ICollection, ICollection<KeyValuePair<TKey, TValue>>, IDeserializationCallback, IDictionary, IDictionary<TKey, TValue>, IEnumerable, IEnumerable<KeyValuePair<TKey, TValue>>, IReadOnlyCollection<KeyValuePair<TKey, TValue>>, IReadOnlyDictionary<TKey, TValue>, ISerializable {
+        public int EnsureCapacity(int capacity);
+        public void TrimExcess();
+        public void TrimExcess(int capacity);
     }
     public class HashSet<T> : ICollection<T>, IDeserializationCallback, IEnumerable, IEnumerable<T>, IReadOnlyCollection<T>, ISerializable, ISet<T> {
+        public int EnsureCapacity(int capacity);
     }
 }