|
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Diagnostics;
namespace System.Linq.Expressions
{
/// <summary>
/// Represents a label, which can be placed in any <see cref="Expression"/> context. If
/// it is jumped to, it will get the value provided by the corresponding
/// <see cref="GotoExpression"/>. Otherwise, it gets the value in <see cref="DefaultValue"/>. If the
/// <see cref="Type"/> equals System.Void, no value should be provided.
/// </summary>
[DebuggerTypeProxy(typeof(LabelExpressionProxy))]
public sealed class LabelExpression : Expression
{
internal LabelExpression(LabelTarget label, Expression? defaultValue)
{
Target = label;
DefaultValue = defaultValue;
}
/// <summary>
/// Gets the static type of the expression that this <see cref="Expression"/> represents. (Inherited from <see cref="Expression"/>.)
/// </summary>
/// <returns>The <see cref="System.Type"/> that represents the static type of the expression.</returns>
public sealed override Type Type => Target.Type;
/// <summary>
/// Returns the node type of this <see cref="Expression"/>. (Inherited from <see cref="Expression"/>.)
/// </summary>
/// <returns>The <see cref="ExpressionType"/> that represents this expression.</returns>
public sealed override ExpressionType NodeType => ExpressionType.Label;
/// <summary>
/// The <see cref="LabelTarget"/> which this label is associated with.
/// </summary>
public LabelTarget Target { get; }
/// <summary>
/// The value of the <see cref="LabelExpression"/> when the label is reached through
/// normal control flow (e.g. is not jumped to).
/// </summary>
public Expression? DefaultValue { get; }
/// <summary>
/// Dispatches to the specific visit method for this node type.
/// </summary>
protected internal override Expression Accept(ExpressionVisitor visitor)
{
return visitor.VisitLabel(this);
}
/// <summary>
/// Creates a new expression that is like this one, but using the
/// supplied children. If all of the children are the same, it will
/// return this expression.
/// </summary>
/// <param name="target">The <see cref="Target"/> property of the result.</param>
/// <param name="defaultValue">The <see cref="DefaultValue"/> property of the result.</param>
/// <returns>This expression if no children changed, or an expression with the updated children.</returns>
public LabelExpression Update(LabelTarget target, Expression? defaultValue)
{
if (target == Target && defaultValue == DefaultValue)
{
return this;
}
return Expression.Label(target, defaultValue);
}
}
public partial class Expression
{
/// <summary>
/// Creates a <see cref="LabelExpression"/> representing a label with no default value.
/// </summary>
/// <param name="target">The <see cref="LabelTarget"/> which this <see cref="LabelExpression"/> will be associated with.</param>
/// <returns>A <see cref="LabelExpression"/> with no default value.</returns>
public static LabelExpression Label(LabelTarget target)
{
return Label(target, defaultValue: null);
}
/// <summary>
/// Creates a <see cref="LabelExpression"/> representing a label with the given default value.
/// </summary>
/// <param name="target">The <see cref="LabelTarget"/> which this <see cref="LabelExpression"/> will be associated with.</param>
/// <param name="defaultValue">The value of this <see cref="LabelExpression"/> when the label is reached through normal control flow.</param>
/// <returns>A <see cref="LabelExpression"/> with the given default value.</returns>
public static LabelExpression Label(LabelTarget target, Expression? defaultValue)
{
ValidateGoto(target, ref defaultValue, nameof(target), nameof(defaultValue), type: null);
return new LabelExpression(target, defaultValue);
}
}
}
|