1 /* ****************************************************************************
3 * Copyright (c) Microsoft Corporation.
5 * This source code is subject to terms and conditions of the Microsoft Public License. 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 Microsoft Public License, 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 Microsoft Public License.
11 * You must not remove this notice, or any other, from this software.
14 * ***************************************************************************/
15 using System; using Microsoft;
18 using System.Diagnostics;
21 namespace System.Linq.Expressions {
23 namespace Microsoft.Linq.Expressions {
26 /// Represents a label, which can be placed in any <see cref="Expression"/> context. If
27 /// it is jumped to, it will get the value provided by the corresponding
28 /// <see cref="GotoExpression"/>. Otherwise, it gets the value in <see cref="LabelExpression.DefaultValue"/>. If the
29 /// <see cref="Type"/> equals System.Void, no value should be provided.
32 [DebuggerTypeProxy(typeof(Expression.LabelExpressionProxy))]
34 public sealed class LabelExpression : Expression {
35 private readonly Expression _defaultValue;
36 private readonly LabelTarget _target;
38 internal LabelExpression(LabelTarget label, Expression defaultValue) {
40 _defaultValue = defaultValue;
44 /// Gets the static type of the expression that this <see cref="Expression" /> represents. (Inherited from <see cref="Expression"/>.)
46 /// <returns>The <see cref="Type"/> that represents the static type of the expression.</returns>
47 public sealed override Type Type {
48 get { return _target.Type; }
52 /// Returns the node type of this <see cref="Expression" />. (Inherited from <see cref="Expression" />.)
54 /// <returns>The <see cref="ExpressionType"/> that represents this expression.</returns>
55 public sealed override ExpressionType NodeType {
56 get { return ExpressionType.Label; }
60 /// The <see cref="LabelTarget"/> which this label is associated with.
62 public LabelTarget Target {
63 get { return _target; }
67 /// The value of the <see cref="LabelExpression"/> when the label is reached through
68 /// normal control flow (e.g. is not jumped to).
70 public Expression DefaultValue {
71 get { return _defaultValue; }
75 /// Dispatches to the specific visit method for this node type.
77 protected internal override Expression Accept(ExpressionVisitor visitor) {
78 return visitor.VisitLabel(this);
82 /// Creates a new expression that is like this one, but using the
83 /// supplied children. If all of the children are the same, it will
84 /// return this expression.
86 /// <param name="target">The <see cref="Target" /> property of the result.</param>
87 /// <param name="defaultValue">The <see cref="DefaultValue" /> property of the result.</param>
88 /// <returns>This expression if no children changed, or an expression with the updated children.</returns>
89 public LabelExpression Update(LabelTarget target, Expression defaultValue) {
90 if (target == Target && defaultValue == DefaultValue) {
93 return Expression.Label(target, defaultValue);
97 public partial class Expression {
99 /// Creates a <see cref="LabelExpression"/> representing a label with no default value.
101 /// <param name="target">The <see cref="LabelTarget"/> which this <see cref="LabelExpression"/> will be associated with.</param>
102 /// <returns>A <see cref="LabelExpression"/> with no default value.</returns>
103 public static LabelExpression Label(LabelTarget target) {
104 return Label(target, null);
108 /// Creates a <see cref="LabelExpression"/> representing a label with the given default value.
110 /// <param name="target">The <see cref="LabelTarget"/> which this <see cref="LabelExpression"/> will be associated with.</param>
111 /// <param name="defaultValue">The value of this <see cref="LabelExpression"/> when the label is reached through normal control flow.</param>
112 /// <returns>A <see cref="LabelExpression"/> with the given default value.</returns>
113 public static LabelExpression Label(LabelTarget target, Expression defaultValue) {
114 ValidateGoto(target, ref defaultValue, "label", "defaultValue");
115 return new LabelExpression(target, defaultValue);