Mysteriously forgot to commit Lexpad.cs at some point in the past. :/

dotnet/runtime/Runtime/Lexpad.cs

@@ -0,0 +1,83 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Rakudo.Metamodel;
+
+namespace Rakudo.Runtime
+{
+    /// <summary>
+    /// Represents a lexpad - either the static version or the dynamic
+    /// one.
+    /// </summary>
+    public struct Lexpad
+    {
+        /// <summary>
+        /// This is the slot mapping, allocating names to slots. All the
+        /// dynamic variants of a lexpad will share this with the static
+        /// lexpad.
+        /// </summary>
+        public Dictionary<string, int> SlotMapping;
+
+        /// <summary>
+        /// The storage assocaited with the lexpad.
+        /// </summary>
+        public RakudoObject[] Storage;
+
+        /// <summary>
+        /// Creates a new static lexpad with the given names all
+        /// allocated slots, in the order they appear in the array.
+        /// </summary>
+        /// <param name="SlotNames"></param>
+        public Lexpad(string[] SlotNames)
+        {
+            SlotMapping = new Dictionary<string, int>(SlotNames.Length);
+            int Slot = 0;
+            foreach (var Name in SlotNames)
+                SlotMapping.Add(Name, Slot++);
+            Storage = new RakudoObject[SlotNames.Length];
+        }
+
+        /// <summary>
+        /// Looks up a lexical by name.
+        /// </summary>
+        /// <param name="Name"></param>
+        /// <returns></returns>
+        public RakudoObject GetByName(string Name)
+        {
+            return Storage[SlotMapping[Name]];
+        }
+
+        /// <summary>
+        /// Sets a lexical by name.
+        /// </summary>
+        /// <param name="Name"></param>
+        /// <returns></returns>
+        public RakudoObject SetByName(string Name, RakudoObject Value)
+        {
+            Storage[SlotMapping[Name]] = Value;
+            return Value;
+        }
+
+        /// <summary>
+        /// Extends the lexpad with an extra slot.
+        /// </summary>
+        /// <param name="Name"></param>
+        public void Extend(string[] Names)
+        {
+            // Add new entry to the mapping. Note that we re-build
+            // it and make it unique to this lexpad now, even if it
+            // was shared before, but add the extra entry.
+            SlotMapping = new Dictionary<string, int>(SlotMapping);
+            int NewSlot = Storage.Length;
+            foreach (var Name in Names)
+                SlotMapping.Add(Name, NewSlot++);
+
+            // Reallocate enlarged storage.
+            var NewStorage = new RakudoObject[Storage.Length + Names.Length];
+            for (int i = 0; i < Storage.Length; i++)
+                NewStorage[i] = Storage[i];
+            Storage = NewStorage;
+        }
+    }
+}