Introduce IdentifierManager to improve PDT evaluator performance.

Assets/Cryville/Common/IdentifierManager.cs

@@ -0,0 +1,45 @@
+using System.Collections.Generic;
+
+namespace Cryville.Common {
+	/// <summary>
+	/// A manager that assigns each given identifiers a unique integer ID.
+	/// </summary>
+	public class IdentifierManager {
+		/// <summary>
+		/// A shared instance of the <see cref="IdentifierManager" /> class.
+		/// </summary>
+		public static IdentifierManager SharedInstance = new IdentifierManager();
+
+		Dictionary<object, int> _idents = new Dictionary<object, int>();
+		List<object> _ids = new List<object>(); 
+
+		object _syncRoot = new object();
+
+		/// <summary>
+		/// Requests an integer ID for an identifier.
+		/// </summary>
+		/// <param name="ident">The identifier.</param>
+		/// <returns>The integer ID.</returns>
+		public int Request(object ident) {
+			lock (_syncRoot) {
+				int id;
+				if (!_idents.TryGetValue(ident, out id)) {
+					_idents.Add(ident, id = _idents.Count);
+					_ids.Add(ident);
+				}
+				return id;
+			}
+		}
+
+		/// <summary>
+		/// Retrieves the identifier assigned with an integer ID.
+		/// </summary>
+		/// <param name="id">The integer ID.</param>
+		/// <returns>The identifier.</returns>
+		public object Retrieve(int id) {
+			lock (_syncRoot) {
+				return _ids[id];
+			}
+		}
+	}
+}