1 /* ****************************************************************************
3 * Copyright (c) Microsoft Corporation.
5 * This source code is subject to terms and conditions of the Apache License, Version 2.0. A
6 * copy of the license can be found in the License.html file at the root of this distribution. If
7 * you cannot locate the Apache License, Version 2.0, please send an email to
8 * dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound
9 * by the terms of the Apache License, Version 2.0.
11 * You must not remove this notice, or any other, from this software.
14 * ***************************************************************************/
17 using System.Diagnostics;
20 namespace Microsoft.Scripting.Ast {
22 namespace System.Linq.Expressions {
25 /// Represents a label, which can be placed in any <see cref="Expression"/> context. If
26 /// it is jumped to, it will get the value provided by the corresponding
27 /// <see cref="GotoExpression"/>. Otherwise, it gets the value in <see cref="LabelExpression.DefaultValue"/>. If the
28 /// <see cref="Type"/> equals System.Void, no value should be provided.
30 [DebuggerTypeProxy(typeof(Expression.LabelExpressionProxy))]
31 public sealed class LabelExpression : Expression {
32 private readonly Expression _defaultValue;
33 private readonly LabelTarget _target;
35 internal LabelExpression(LabelTarget label, Expression defaultValue) {
37 _defaultValue = defaultValue;
41 /// Gets the static type of the expression that this <see cref="Expression" /> represents. (Inherited from <see cref="Expression"/>.)
43 /// <returns>The <see cref="Type"/> that represents the static type of the expression.</returns>
44 public sealed override Type Type {
45 get { return _target.Type; }
49 /// Returns the node type of this <see cref="Expression" />. (Inherited from <see cref="Expression" />.)
51 /// <returns>The <see cref="ExpressionType"/> that represents this expression.</returns>
52 public sealed override ExpressionType NodeType {
53 get { return ExpressionType.Label; }
57 /// The <see cref="LabelTarget"/> which this label is associated with.
59 public LabelTarget Target {
60 get { return _target; }
64 /// The value of the <see cref="LabelExpression"/> when the label is reached through
65 /// normal control flow (e.g. is not jumped to).
67 public Expression DefaultValue {
68 get { return _defaultValue; }
72 /// Dispatches to the specific visit method for this node type.
74 protected internal override Expression Accept(ExpressionVisitor visitor) {
75 return visitor.VisitLabel(this);
79 /// Creates a new expression that is like this one, but using the
80 /// supplied children. If all of the children are the same, it will
81 /// return this expression.
83 /// <param name="target">The <see cref="Target" /> property of the result.</param>
84 /// <param name="defaultValue">The <see cref="DefaultValue" /> property of the result.</param>
85 /// <returns>This expression if no children changed, or an expression with the updated children.</returns>
86 public LabelExpression Update(LabelTarget target, Expression defaultValue) {
87 if (target == Target && defaultValue == DefaultValue) {
90 return Expression.Label(target, defaultValue);
94 public partial class Expression {
96 /// Creates a <see cref="LabelExpression"/> representing a label with no default value.
98 /// <param name="target">The <see cref="LabelTarget"/> which this <see cref="LabelExpression"/> will be associated with.</param>
99 /// <returns>A <see cref="LabelExpression"/> with no default value.</returns>
100 public static LabelExpression Label(LabelTarget target) {
101 return Label(target, null);
105 /// Creates a <see cref="LabelExpression"/> representing a label with the given default value.
107 /// <param name="target">The <see cref="LabelTarget"/> which this <see cref="LabelExpression"/> will be associated with.</param>
108 /// <param name="defaultValue">The value of this <see cref="LabelExpression"/> when the label is reached through normal control flow.</param>
109 /// <returns>A <see cref="LabelExpression"/> with the given default value.</returns>
110 public static LabelExpression Label(LabelTarget target, Expression defaultValue) {
111 ValidateGoto(target, ref defaultValue, "label", "defaultValue");
112 return new LabelExpression(target, defaultValue);