Make AstNode freezable.

ICSharpCode.NRefactory.CSharp/Ast/AstNode.cs

@@ -33,12 +33,10 @@ using System.Threading;
 
 namespace ICSharpCode.NRefactory.CSharp
 {
-	public abstract class AstNode : AbstractAnnotatable, PatternMatching.INode
+	public abstract class AstNode : AbstractAnnotatable, ICSharpCode.NRefactory.TypeSystem.IFreezable, PatternMatching.INode
 	{
-		/// <summary>
-		/// Root of an abstract syntax tree.
-		/// </summary>
-		public static readonly Role<AstNode> Root = new Role<AstNode> ("Root");
+		// the Root role must be available when creating the null nodes, so we can't put it in the Roles class
+		internal static readonly Role<AstNode> RootRole = new Role<AstNode> ("Root");
 		
 		#region Null
 		public static readonly AstNode Null = new NullAstNode ();
@@ -129,7 +127,42 @@ namespace ICSharpCode.NRefactory.CSharp
 		AstNode nextSibling;
 		AstNode firstChild;
 		AstNode lastChild;
-		Role role = Root;
+		
+		// Flags, from least significant to most significant bits:
+		// - Role.RoleIndexBits: role index
+		// - 1 bit: IsFrozen
+		protected uint flags = RootRole.Index;
+		// Derived classes may also use a few bits,
+		// for example Identifier uses 1 bit for IsVerbatim
+		
+		const uint roleIndexMask = (1u << Role.RoleIndexBits) - 1;
+		const uint frozenBit = 1u << Role.RoleIndexBits;
+		protected const int AstNodeFlagsUsedBits = Role.RoleIndexBits + 1;
+		
+		protected AstNode()
+		{
+			if (IsNull)
+				Freeze();
+		}
+		
+		public bool IsFrozen {
+			get { return (flags & frozenBit) != 0; }
+		}
+		
+		public void Freeze()
+		{
+			if (!IsFrozen) {
+				for (AstNode child = firstChild; child != null; child = child.nextSibling)
+					child.Freeze();
+				flags |= frozenBit;
+			}
+		}
+		
+		protected void ThrowIfFrozen()
+		{
+			if (IsFrozen)
+				throw new InvalidOperationException("Cannot mutate frozen " + GetType().Name);
+		}
 		
 		public abstract NodeType NodeType {
 			get;
@@ -176,16 +209,24 @@ namespace ICSharpCode.NRefactory.CSharp
 		}
 		
 		public Role Role {
-			get { return role; }
+			get {
+				return Role.GetByIndex(flags & roleIndexMask);
+			}
 			set {
 				if (value == null)
 					throw new ArgumentNullException("value");
 				if (!value.IsValid(this))
 					throw new ArgumentException("This node is not valid in the new role.");
-				role = value;
+				ThrowIfFrozen();
+				SetRole(value);
 			}
 		}
 		
+		void SetRole(Role role)
+		{
+			flags = (flags & ~roleIndexMask) | role.Index;
+		}
+		
 		public AstNode NextSibling {
 			get { return nextSibling; }
 		}
@@ -258,8 +299,9 @@ namespace ICSharpCode.NRefactory.CSharp
 		{
 			if (role == null)
 				throw new ArgumentNullException ("role");
+			uint roleIndex = role.Index;
 			for (var cur = firstChild; cur != null; cur = cur.nextSibling) {
-				if (cur.role == role)
+				if ((cur.flags & roleIndexMask) == roleIndex)
 					return (T)cur;
 			}
 			return role.NullObject;
@@ -285,10 +327,11 @@ namespace ICSharpCode.NRefactory.CSharp
 				throw new ArgumentNullException ("role");
 			if (child == null || child.IsNull)
 				return;
-			if (this.IsNull)
-				throw new InvalidOperationException ("Cannot add children to null nodes");
+			ThrowIfFrozen();
 			if (child.parent != null)
 				throw new ArgumentException ("Node is already used in another tree.", "child");
+			if (child.IsFrozen)
+				throw new ArgumentException ("Cannot add a frozen node.", "child");
 			AddChildUnsafe (child, role);
 		}
 		
@@ -298,7 +341,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		void AddChildUnsafe (AstNode child, Role role)
 		{
 			child.parent = this;
-			child.role = role;
+			child.SetRole(role);
 			if (firstChild == null) {
 				lastChild = firstChild = child;
 			} else {
@@ -319,8 +362,11 @@ namespace ICSharpCode.NRefactory.CSharp
 			
 			if (child == null || child.IsNull)
 				return;
+			ThrowIfFrozen();
 			if (child.parent != null)
 				throw new ArgumentException ("Node is already used in another tree.", "child");
+			if (child.IsFrozen)
+				throw new ArgumentException ("Cannot add a frozen node.", "child");
 			if (nextSibling.parent != this)
 				throw new ArgumentException ("NextSibling is not a child of this node.", "nextSibling");
 			// No need to test for "Cannot add children to null nodes",
@@ -331,7 +377,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		void InsertChildBeforeUnsafe (AstNode nextSibling, AstNode child, Role role)
 		{
 			child.parent = this;
-			child.role = role;
+			child.SetRole(role);
 			child.nextSibling = nextSibling;
 			child.prevSibling = nextSibling.prevSibling;
 			
@@ -356,6 +402,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		public void Remove ()
 		{
 			if (parent != null) {
+				ThrowIfFrozen();
 				if (prevSibling != null) {
 					Debug.Assert (prevSibling.nextSibling == this);
 					prevSibling.nextSibling = nextSibling;
@@ -390,10 +437,11 @@ namespace ICSharpCode.NRefactory.CSharp
 			if (parent == null) {
 				throw new InvalidOperationException (this.IsNull ? "Cannot replace the null nodes" : "Cannot replace the root node");
 			}
+			ThrowIfFrozen();
 			// Because this method doesn't statically check the new node's type with the role,
 			// we perform a runtime test:
-			if (!role.IsValid (newNode)) {
-				throw new ArgumentException (string.Format ("The new node '{0}' is not valid in the role {1}", newNode.GetType ().Name, role.ToString ()), "newNode");
+			if (!this.Role.IsValid (newNode)) {
+				throw new ArgumentException (string.Format ("The new node '{0}' is not valid in the role {1}", newNode.GetType ().Name, this.Role.ToString ()), "newNode");
 			}
 			if (newNode.parent != null) {
 				// newNode is used within this tree?
@@ -405,9 +453,11 @@ namespace ICSharpCode.NRefactory.CSharp
 					throw new ArgumentException ("Node is already used in another tree.", "newNode");
 				}
 			}
+			if (newNode.IsFrozen)
+				throw new ArgumentException ("Cannot add a frozen node.", "newNode");
 			
 			newNode.parent = parent;
-			newNode.role = role;
+			newNode.SetRole(this.Role);
 			newNode.prevSibling = prevSibling;
 			newNode.nextSibling = nextSibling;
 			if (parent != null) {
@@ -440,7 +490,7 @@ namespace ICSharpCode.NRefactory.CSharp
 			}
 			AstNode oldParent = parent;
 			AstNode oldSuccessor = nextSibling;
-			Role oldRole = role;
+			Role oldRole = this.Role;
 			Remove ();
 			AstNode replacement = replaceFunction (this);
 			if (oldSuccessor != null && oldSuccessor.parent != oldParent)
@@ -473,10 +523,11 @@ namespace ICSharpCode.NRefactory.CSharp
 			copy.lastChild = null;
 			copy.prevSibling = null;
 			copy.nextSibling = null;
+			copy.flags &= ~frozenBit; // unfreeze the copy
 			
 			// Then perform a deep copy:
 			for (AstNode cur = firstChild; cur != null; cur = cur.nextSibling) {
-				copy.AddChildUnsafe (cur.Clone (), cur.role);
+				copy.AddChildUnsafe (cur.Clone (), cur.Role);
 			}
 			
 			// Finally, clone the annotation, if necessary

ICSharpCode.NRefactory.CSharp/Ast/CSharpModifierToken.cs

@@ -29,14 +29,16 @@ using System.Linq;
 
 namespace ICSharpCode.NRefactory.CSharp
 {
-	
 	public class CSharpModifierToken : CSharpTokenNode
 	{
 		Modifiers modifier;
 		
 		public Modifiers Modifier {
 			get { return modifier; }
-			set { this.modifier = value; }
+			set { 
+				ThrowIfFrozen();
+				this.modifier = value; 
+			}
 		}
 		
 		protected override int TokenLength {

ICSharpCode.NRefactory.CSharp/Ast/CSharpTokenNode.cs

@@ -103,6 +103,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		#region IRelocationable implementation
 		void IRelocatable.SetStartLocation (TextLocation startLocation)
 		{
+			ThrowIfFrozen();
 			this.startLocation = startLocation;
 		}
 		#endregion

ICSharpCode.NRefactory.CSharp/Ast/CompilationUnit.cs

@@ -1,4 +1,4 @@
-// 
+// 
 // CompilationUnit.cs
 //
 // Author:
@@ -45,10 +45,18 @@ namespace ICSharpCode.NRefactory.CSharp
 			}
 		}
 		
+		string fileName;
+		
 		/// <summary>
 		/// Gets/Sets the file name of this compilation unit.
 		/// </summary>
-		public string FileName { get; set; }
+		public string FileName {
+			get { return fileName; }
+			set {
+				ThrowIfFrozen();
+				fileName = value;
+			}
+		}
 		
 		List<Error> errors = new List<Error> ();
 		
@@ -83,7 +91,7 @@ namespace ICSharpCode.NRefactory.CSharp
 				}
 				foreach (var child in curNode.Children) {
 					if (!(child is Statement || child is Expression) &&
-						(child.Role != Roles.TypeMemberRole || (child is TypeDeclaration && includeInnerTypes)))
+					    (child.Role != Roles.TypeMemberRole || (child is TypeDeclaration && includeInnerTypes)))
 						nodeStack.Push (child);
 				}
 			}
@@ -99,7 +107,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		{
 			visitor.VisitCompilationUnit (this);
 		}
-			
+		
 		public override T AcceptVisitor<T> (IAstVisitor<T> visitor)
 		{
 			return visitor.VisitCompilationUnit (this);

ICSharpCode.NRefactory.CSharp/Ast/DocumentationReference.cs

@@ -29,6 +29,10 @@ namespace ICSharpCode.NRefactory.CSharp
 		public static readonly Role<AstType> DeclaringTypeRole = new Role<AstType>("DeclaringType", AstType.Null);
 		public static readonly Role<AstType> ConversionOperatorReturnTypeRole = new Role<AstType>("ConversionOperatorReturnType", AstType.Null);
 		
+		EntityType entityType;
+		OperatorType operatorType;
+		bool hasParameterList;
+		
 		/// <summary>
 		/// Gets/Sets the entity type.
 		/// Possible values are:
@@ -37,18 +41,36 @@ namespace ICSharpCode.NRefactory.CSharp
 		///   <c>EntityType.TypeDefinition</c> for references to primitive types,
 		///   and <c>EntityType.None</c> for everything else.
 		/// </summary>
-		public EntityType EntityType { get; set; }
+		public EntityType EntityType {
+			get { return entityType; }
+			set {
+				ThrowIfFrozen();
+				entityType = value;
+			}
+		}
 		
 		/// <summary>
 		/// Gets/Sets the operator type.
 		/// This property is only used when EntityType==Operator.
 		/// </summary>
-		public OperatorType OperatorType { get; set; }
+		public OperatorType OperatorType {
+			get { return operatorType; }
+			set {
+				ThrowIfFrozen();
+				operatorType = value;
+			}
+		}
 		
 		/// <summary>
 		/// Gets/Sets whether a parameter list was provided.
 		/// </summary>
-		public bool HasParameterList { get; set; }
+		public bool HasParameterList {
+			get { return hasParameterList; }
+			set {
+				ThrowIfFrozen();
+				hasParameterList = value;
+			}
+		}
 		
 		public override NodeType NodeType {
 			get { return NodeType.Unknown; }
@@ -113,7 +135,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		{
 			visitor.VisitDocumentationReference (this);
 		}
-			
+		
 		public override T AcceptVisitor<T> (IAstVisitor<T> visitor)
 		{
 			return visitor.VisitDocumentationReference (this);

ICSharpCode.NRefactory.CSharp/Ast/Expressions/AnonymousMethodExpression.cs

@@ -37,11 +37,19 @@ namespace ICSharpCode.NRefactory.CSharp
 		public readonly static TokenRole DelegateKeywordRole = new TokenRole ("delegate");
 		public readonly static TokenRole AsyncModifierRole = LambdaExpression.AsyncModifierRole;
 		
-		public bool IsAsync { get; set; }
+		bool isAsync;
+		
+		public bool IsAsync {
+			get { return isAsync; }
+			set { ThrowIfFrozen(); isAsync = value; }
+		}
 		
 		// used to tell the difference between delegate {} and delegate () {}
+		bool hasParameterList;
+		
 		public bool HasParameterList {
-			get; set;
+			get { return hasParameterList; }
+			set { ThrowIfFrozen(); hasParameterList = value; }
 		}
 		
 		public CSharpTokenNode DelegateToken {

ICSharpCode.NRefactory.CSharp/Ast/Expressions/EmptyExpression.cs

@@ -58,6 +58,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		#region IRelocationable implementation
 		void IRelocatable.SetStartLocation (TextLocation startLocation)
 		{
+			ThrowIfFrozen();
 			this.location = startLocation;
 		}
 		#endregion

ICSharpCode.NRefactory.CSharp/Ast/Expressions/LambdaExpression.cs

@@ -37,7 +37,12 @@ namespace ICSharpCode.NRefactory.CSharp
 		public readonly static TokenRole ArrowRole = new TokenRole ("=>");
 		public static readonly Role<AstNode> BodyRole = new Role<AstNode>("Body", AstNode.Null);
 		
-		public bool IsAsync { get; set; }
+		bool isAsync;
+		
+		public bool IsAsync {
+			get { return isAsync; }
+			set { ThrowIfFrozen(); isAsync = value; }
+		}
 		
 		public AstNodeCollection<ParameterDeclaration> Parameters {
 			get { return GetChildrenByRole (Roles.Parameter); }

ICSharpCode.NRefactory.CSharp/Ast/Expressions/PrimitiveExpression.cs

@@ -47,14 +47,21 @@ namespace ICSharpCode.NRefactory.CSharp
 			}
 		}
 		
+		object value;
+		
 		public object Value {
-			get;
-			set;
+			get { return this.value; }
+			set { 
+				ThrowIfFrozen(); 
+				this.value = value;
+			}
 		}
 		
 		public string LiteralValue {
-			get {
-				return literalValue;
+			get { return literalValue; }
+			set {
+				ThrowIfFrozen();
+				literalValue = value;
 			}
 		}
 		

ICSharpCode.NRefactory.CSharp/Ast/GeneralScope/Comment.cs

@@ -58,19 +58,25 @@ namespace ICSharpCode.NRefactory.CSharp
 			}
 		}
 		
+		CommentType commentType;
+		
 		public CommentType CommentType {
-			get;
-			set;
+			get { return commentType; }
+			set { ThrowIfFrozen(); commentType = value; }
 		}
 		
+		bool startsLine;
+		
 		public bool StartsLine {
-			get;
-			set;
+			get { return startsLine; }
+			set { ThrowIfFrozen(); startsLine = value; }
 		}
 		
+		string content;
+		
 		public string Content {
-			get;
-			set;
+			get { return content; }
+			set { ThrowIfFrozen(); content = value; }
 		}
 		
 		TextLocation startLocation;
@@ -103,6 +109,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		#region IRelocationable implementation
 		void IRelocatable.SetStartLocation (TextLocation startLocation)
 		{
+			ThrowIfFrozen();
 			int lineDelta = startLocation.Line - this.startLocation.Line;
 			endLocation = new TextLocation (endLocation.Line + lineDelta, lineDelta != 0 ? endLocation.Column : endLocation.Column + startLocation.Column - this.startLocation.Column);
 			this.startLocation = startLocation;

ICSharpCode.NRefactory.CSharp/Ast/GeneralScope/PreProcessorDirective.cs

@@ -96,6 +96,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		#region IRelocationable implementation
 		void IRelocatable.SetStartLocation (TextLocation startLocation)
 		{
+			ThrowIfFrozen();
 			int lineDelta = startLocation.Line - this.startLocation.Line;
 			endLocation = new TextLocation (endLocation.Line + lineDelta, lineDelta != 0 ? endLocation.Column : endLocation.Column + startLocation.Column - this.startLocation.Column);
 			this.startLocation = startLocation;

ICSharpCode.NRefactory.CSharp/Ast/GeneralScope/TypeDeclaration.cs

@@ -114,17 +114,17 @@ namespace ICSharpCode.NRefactory.CSharp
 
 		public static TypeDeclaration Create(ClassType type)
 		{
-			switch (type) {
-				case ICSharpCode.NRefactory.CSharp.ClassType.Class:
+			switch (type) {
+				case ICSharpCode.NRefactory.CSharp.ClassType.Class:
 					return new Class ();
-				case ICSharpCode.NRefactory.CSharp.ClassType.Struct:
+				case ICSharpCode.NRefactory.CSharp.ClassType.Struct:
 					return new Struct ();
-				case ICSharpCode.NRefactory.CSharp.ClassType.Interface:
+				case ICSharpCode.NRefactory.CSharp.ClassType.Interface:
 					return new Interface ();
-				case ICSharpCode.NRefactory.CSharp.ClassType.Enum:
+				case ICSharpCode.NRefactory.CSharp.ClassType.Enum:
 					return new Enum ();
-				default:
-					throw new System.ArgumentOutOfRangeException();
+				default:
+					throw new System.ArgumentOutOfRangeException();
 			}
 		}
 

ICSharpCode.NRefactory.CSharp/Ast/GeneralScope/TypeParameterDeclaration.cs

@@ -42,8 +42,11 @@ namespace ICSharpCode.NRefactory.CSharp
 			get { return GetChildrenByRole (AttributeRole); }
 		}
 		
+		VarianceModifier variance;
+		
 		public VarianceModifier Variance {
-			get; set;
+			get { return variance; }
+			set { ThrowIfFrozen(); variance = value; }
 		}
 		
 		public CSharpTokenNode VarianceToken {

ICSharpCode.NRefactory.CSharp/Ast/Identifier.cs

@@ -1,6 +1,6 @@
 // 
 // Identifier.cs
-//  
+//
 // Author:
 //       Mike Krüger <mkrueger@novell.com>
 // 
@@ -42,7 +42,7 @@ namespace ICSharpCode.NRefactory.CSharp
 			public override void AcceptVisitor (IAstVisitor visitor)
 			{
 			}
-				
+			
 			public override T AcceptVisitor<T> (IAstVisitor<T> visitor)
 			{
 				return default (T);
@@ -68,9 +68,10 @@ namespace ICSharpCode.NRefactory.CSharp
 		string name;
 		public string Name {
 			get { return this.name; }
-			set { 
+			set {
 				if (value == null)
 					throw new ArgumentNullException("value");
+				ThrowIfFrozen();
 				this.name = value;
 			}
 		}
@@ -80,25 +81,34 @@ namespace ICSharpCode.NRefactory.CSharp
 			get {
 				return startLocation;
 			}
-			
 		}
 		
-		public virtual bool IsVerbatim {
+		const uint verbatimBit = 1u << AstNodeFlagsUsedBits;
+		
+		public bool IsVerbatim {
 			get {
-				return false;
+				return (flags & verbatimBit) != 0;
+			}
+			set {
+				ThrowIfFrozen();
+				if (value)
+					flags |= verbatimBit;
+				else
+					flags &= ~verbatimBit;
 			}
 		}
 		
 		#region IRelocationable implementation
 		void IRelocatable.SetStartLocation (TextLocation startLocation)
 		{
+			ThrowIfFrozen();
 			this.startLocation = startLocation;
 		}
 		#endregion
 		
 		public override TextLocation EndLocation {
 			get {
-				return new TextLocation (StartLocation.Line, StartLocation.Column + (Name ?? "").Length);
+				return new TextLocation (StartLocation.Line, StartLocation.Column + (Name ?? "").Length + (IsVerbatim ? 1 : 0));
 			}
 		}
 		
@@ -125,7 +135,7 @@ namespace ICSharpCode.NRefactory.CSharp
 			if (string.IsNullOrEmpty(name))
 				return Identifier.Null;
 			if (name[0] == '@')
-				return new VerbatimIdentifier(name.Substring (1), location);
+				return new Identifier (name.Substring (1), location) { IsVerbatim = true };
 			else
 				return new Identifier (name, location);
 		}
@@ -136,7 +146,7 @@ namespace ICSharpCode.NRefactory.CSharp
 				return Identifier.Null;
 			
 			if (isVerbatim)
-				return new VerbatimIdentifier (name, location);
+				return new Identifier (name, location) { IsVerbatim = true };
 			return new Identifier (name, location);
 		}
 		
@@ -144,7 +154,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		{
 			visitor.VisitIdentifier (this);
 		}
-			
+		
 		public override T AcceptVisitor<T> (IAstVisitor<T> visitor)
 		{
 			return visitor.VisitIdentifier (this);
@@ -160,24 +170,5 @@ namespace ICSharpCode.NRefactory.CSharp
 			Identifier o = other as Identifier;
 			return o != null && !o.IsNull && MatchString(this.Name, o.Name);
 		}
-
-		class VerbatimIdentifier : Identifier
-		{
-			public override TextLocation EndLocation {
-				get {
-					return new TextLocation (StartLocation.Line, StartLocation.Column + (Name ?? "").Length + 1); // @"..."
-				}
-			}
-			
-			public override bool IsVerbatim {
-				get {
-					return true;
-				}
-			}
-			
-			public VerbatimIdentifier(string name, TextLocation location) : base (name, location)
-			{
-			}
-		}
 	}
 }

ICSharpCode.NRefactory.CSharp/Ast/MemberType.cs

@@ -37,7 +37,15 @@ namespace ICSharpCode.NRefactory.CSharp
 	{
 		public static readonly Role<AstType> TargetRole = new Role<AstType>("Target", AstType.Null);
 		
-		public bool IsDoubleColon { get; set; }
+		bool isDoubleColon;
+		
+		public bool IsDoubleColon {
+			get { return isDoubleColon; }
+			set {
+				ThrowIfFrozen();
+				isDoubleColon = value;
+			}
+		}
 		
 		public AstType Target {
 			get { return GetChildByRole(TargetRole); }
@@ -93,7 +101,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		{
 			visitor.VisitMemberType (this);
 		}
-			
+		
 		public override T AcceptVisitor<T> (IAstVisitor<T> visitor)
 		{
 			return visitor.VisitMemberType (this);

ICSharpCode.NRefactory.CSharp/Ast/PrimitiveType.cs

@@ -34,8 +34,18 @@ namespace ICSharpCode.NRefactory.CSharp
 {
 	public class PrimitiveType : AstType, IRelocatable
 	{
-		public string Keyword { get; set; }
-		public TextLocation Location { get; set; }
+		TextLocation location;
+		string keyword = string.Empty;
+		
+		public string Keyword {
+			get { return keyword; }
+			set { 
+				if (value == null)
+					throw new ArgumentNullException();
+				ThrowIfFrozen();
+				keyword = value; 
+			}
+		}
 		
 		public KnownTypeCode KnownTypeCode {
 			get { return GetTypeCodeForPrimitiveType(this.Keyword); }
@@ -53,17 +63,17 @@ namespace ICSharpCode.NRefactory.CSharp
 		public PrimitiveType(string keyword, TextLocation location)
 		{
 			this.Keyword = keyword;
-			this.Location = location;
+			this.location = location;
 		}
 		
 		public override TextLocation StartLocation {
 			get {
-				return Location;
+				return location;
 			}
 		}
 		public override TextLocation EndLocation {
 			get {
-				return new TextLocation (Location.Line, Location.Column + (Keyword != null ? Keyword.Length : 0));
+				return new TextLocation (location.Line, location.Column + keyword.Length);
 			}
 		}
 		
@@ -71,7 +81,8 @@ namespace ICSharpCode.NRefactory.CSharp
 		#region IRelocationable implementation
 		void IRelocatable.SetStartLocation (TextLocation startLocation)
 		{
-			this.Location = startLocation;
+			ThrowIfFrozen();
+			this.location = startLocation;
 		}
 		#endregion
 		
@@ -98,7 +109,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		
 		public override string ToString()
 		{
-			return Keyword ?? base.ToString();
+			return Keyword;
 		}
 		
 		public override ITypeReference ToTypeReference(SimpleNameLookupMode lookupMode = SimpleNameLookupMode.Type)

ICSharpCode.NRefactory.CSharp/Ast/Roles.cs

@@ -1,4 +1,4 @@
-// 
+// 
 // Roles.cs
 //  
 // Author:
@@ -30,7 +30,8 @@ namespace ICSharpCode.NRefactory.CSharp
 {
 	public static class Roles
 	{
-			
+		public static readonly Role<AstNode> Root = AstNode.RootRole;
+		
 		// some pre defined constants for common roles
 		public static readonly Role<Identifier> Identifier = new Role<Identifier> ("Identifier", CSharp.Identifier.Null);
 		public static readonly Role<BlockStatement> Body = new Role<BlockStatement> ("Body", CSharp.BlockStatement.Null);

ICSharpCode.NRefactory.CSharp/Ast/Statements/EmptyStatement.cs

@@ -51,6 +51,7 @@ namespace ICSharpCode.NRefactory.CSharp
 		#region IRelocationable implementation
 		void IRelocatable.SetStartLocation (TextLocation startLocation)
 		{
+			ThrowIfFrozen();
 			this.Location = startLocation;
 		}
 		#endregion

ICSharpCode.NRefactory.CSharp/Ast/TypeMembers/OperatorDeclaration.cs

@@ -109,9 +109,14 @@ namespace ICSharpCode.NRefactory.CSharp
 			get { return EntityType.Operator; }
 		}
 		
+		OperatorType operatorType;
+		
 		public OperatorType OperatorType {
-			get;
-			set;
+			get { return operatorType; }
+			set {
+				ThrowIfFrozen();
+				operatorType = value;
+			}
 		}
 		
 		public CSharpTokenNode OperatorToken {

ICSharpCode.NRefactory.CSharp/Ast/TypeMembers/ParameterDeclaration.cs

@@ -56,9 +56,14 @@ namespace ICSharpCode.NRefactory.CSharp
 			get { return GetChildrenByRole (AttributeRole); }
 		}
 		
+		ParameterModifier parameterModifier;
+		
 		public ParameterModifier ParameterModifier {
-			get;
-			set;
+			get { return parameterModifier; }
+			set {
+				ThrowIfFrozen();
+				parameterModifier = value;
+			}
 		}
 		
 		public AstType Type {

ICSharpCode.NRefactory.Tests/CSharp/ContextAction/TestRefactoringContext.cs

@@ -137,6 +137,7 @@ namespace ICSharpCode.NRefactory.CSharp.ContextActions
 			if (parser.HasErrors)
 				parser.ErrorPrinter.Errors.ForEach (e => Console.WriteLine (e.Message));
 			Assert.IsFalse (parser.HasErrors, "File contains parsing errors.");
+			unit.Freeze();
 			var parsedFile = unit.ToTypeSystem();
 			
 			IProjectContent pc = new CSharpProjectContent();

ICSharpCode.NRefactory.Tests/CSharp/Resolver/FindReferencesTest.cs

@@ -129,5 +129,23 @@ class Test {
 			Assert.IsTrue(actual.Any(r => r.StartLocation.Line == 3 && r is MethodDeclaration));
 			Assert.IsTrue(actual.Any(r => r.StartLocation.Line == 8 && r is ForeachStatement));
 		}
+		
+		[Test]
+		public void FindReferencesForOpImplicitInLocalVariableInitialization()
+		{
+			Init(@"using System;
+class Test {
+ static void T() {
+  int x = new Test();
+ }
+ public static implicit operator int(Test x) { return 0; }
+}");
+			var test = compilation.MainAssembly.TopLevelTypeDefinitions.Single(t => t.Name == "Test");
+			var opImplicit = test.Methods.Single(m => m.Name == "op_Implicit");
+			var actual = FindReferences(opImplicit).ToList();
+			Assert.AreEqual(2, actual.Count);
+			Assert.IsTrue(actual.Any(r => r.StartLocation.Line == 4 && r is ObjectCreateExpression));
+			Assert.IsTrue(actual.Any(r => r.StartLocation.Line == 6 && r is OperatorDeclaration));
+		}
 	}
 }

ICSharpCode.NRefactory/Role.cs

@@ -17,6 +17,7 @@
 // DEALINGS IN THE SOFTWARE.
 
 using System;
+using System.Threading;
 
 namespace ICSharpCode.NRefactory
 {
@@ -25,12 +26,40 @@ namespace ICSharpCode.NRefactory
 	/// </summary>
 	public abstract class Role
 	{
-		internal Role() {} // don't allow NRefactory consumers to derive from Role
+		public const int RoleIndexBits = 9;
+		
+		static readonly Role[] roles = new Role[1 << RoleIndexBits];
+		static int nextRoleIndex = 0;
+		
+		readonly uint index;
+		
+		[CLSCompliant(false)]
+		public uint Index {
+			get { return index; }
+		}
+		
+		// don't allow NRefactory consumers to derive from Role
+		internal Role()
+		{
+			this.index = (uint)Interlocked.Increment(ref nextRoleIndex);
+			if (this.index >= roles.Length)
+				throw new InvalidOperationException("");
+			roles[this.index] = this;
+		}
 		
 		/// <summary>
 		/// Gets whether the specified node is valid in this role.
 		/// </summary>
 		public abstract bool IsValid(object node);
+		
+		/// <summary>
+		/// Gets the role with the specified index.
+		/// </summary>
+		[CLSCompliant(false)]
+		public static Role GetByIndex(uint index)
+		{
+			return roles[index];
+		}
 	}
 	
 	/// <summary>