THRIFT-4879 general performance improvements for netstd library
Client: netstd
Patch: Jens Geyer

This closes #1808
diff --git a/lib/netstd/Thrift/Collections/THashSet.cs b/lib/netstd/Thrift/Collections/THashSet.cs
index 011f0a0..ffab577 100644
--- a/lib/netstd/Thrift/Collections/THashSet.cs
+++ b/lib/netstd/Thrift/Collections/THashSet.cs
@@ -23,45 +23,56 @@
     // ReSharper disable once InconsistentNaming
     public class THashSet<T> : ICollection<T>
     {
-        private readonly HashSet<T> _set = new HashSet<T>();
+        private readonly HashSet<T> Items;
 
-        public int Count => _set.Count;
+        public THashSet()
+        {
+            Items = new HashSet<T>();
+        }
+
+        public THashSet(int capacity)
+        {
+            // TODO: uncomment capacity when NET Standard also implements it
+            Items = new HashSet<T>(/*capacity*/);
+        }
+
+        public int Count => Items.Count;
 
         public bool IsReadOnly => false;
 
         public void Add(T item)
         {
-            _set.Add(item);
+            Items.Add(item);
         }
 
         public void Clear()
         {
-            _set.Clear();
+            Items.Clear();
         }
 
         public bool Contains(T item)
         {
-            return _set.Contains(item);
+            return Items.Contains(item);
         }
 
         public void CopyTo(T[] array, int arrayIndex)
         {
-            _set.CopyTo(array, arrayIndex);
+            Items.CopyTo(array, arrayIndex);
         }
 
         public IEnumerator GetEnumerator()
         {
-            return _set.GetEnumerator();
+            return Items.GetEnumerator();
         }
 
         IEnumerator<T> IEnumerable<T>.GetEnumerator()
         {
-            return ((IEnumerable<T>) _set).GetEnumerator();
+            return ((IEnumerable<T>) Items).GetEnumerator();
         }
 
         public bool Remove(T item)
         {
-            return _set.Remove(item);
+            return Items.Remove(item);
         }
     }
-}
\ No newline at end of file
+}