1 files changed, 81 insertions, 0 deletions
diff --git a/src/mscorlib/src/System/ParamsArray.cs b/src/mscorlib/src/System/ParamsArray.cs
new file mode 100644
index 0000000000..ed8919c586
--- /dev/null
+++ b/src/mscorlib/src/System/ParamsArray.cs
@@ -0,0 +1,81 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+namespace System
+{
+    internal struct ParamsArray
+    {
+        // Sentinel fixed-length arrays eliminate the need for a "count" field keeping this
+        // struct down to just 4 fields. These are only used for their "Length" property,
+        // that is, their elements are never set or referenced.
+        private static readonly object[] oneArgArray = new object[1];
+        private static readonly object[] twoArgArray = new object[2];
+        private static readonly object[] threeArgArray = new object[3];
+
+        private readonly object arg0;
+        private readonly object arg1;
+        private readonly object arg2;
+
+        // After construction, the first three elements of this array will never be accessed
+        // because the indexer will retrieve those values from arg0, arg1, and arg2.
+        private readonly object[] args;
+
+        public ParamsArray(object arg0)
+        {
+            this.arg0 = arg0;
+            this.arg1 = null;
+            this.arg2 = null;
+
+            // Always assign this.args to make use of its "Length" property
+            this.args = oneArgArray;
+        }
+
+        public ParamsArray(object arg0, object arg1)
+        {
+            this.arg0 = arg0;
+            this.arg1 = arg1;
+            this.arg2 = null;
+
+            // Always assign this.args to make use of its "Length" property
+            this.args = twoArgArray;
+        }
+
+        public ParamsArray(object arg0, object arg1, object arg2)
+        {
+            this.arg0 = arg0;
+            this.arg1 = arg1;
+            this.arg2 = arg2;
+
+            // Always assign this.args to make use of its "Length" property
+            this.args = threeArgArray;
+        }
+
+        public ParamsArray(object[] args)
+        {
+            int len = args.Length;
+            this.arg0 = len > 0 ? args[0] : null;
+            this.arg1 = len > 1 ? args[1] : null;
+            this.arg2 = len > 2 ? args[2] : null;
+            this.args = args;
+        }
+
+        public int Length
+        {
+            get { return this.args.Length; }
+        }
+
+        public object this[int index]
+        {
+            get { return index == 0 ? this.arg0 : GetAtSlow(index); }
+        }
+
+        private object GetAtSlow(int index)
+        {
+            if (index == 1)
+                return this.arg1;
+            if (index == 2)
+                return this.arg2;
+            return this.args[index];
+        }
+    }
+}