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// 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;
using System.Dynamic.Utils;
namespace System.Linq.Expressions
{
/// <summary>
/// Represents the default value of a type or an empty expression.
/// </summary>
[DebuggerTypeProxy(typeof(DefaultExpressionProxy))]
public sealed class DefaultExpression : Expression
{
internal DefaultExpression(Type type)
{
Type = type;
}
/// <summary>
/// Gets the static type of the expression that this <see cref="Expression"/> represents.
/// </summary>
/// <returns>The <see cref="System.Type"/> that represents the static type of the expression.</returns>
public sealed override Type Type { get; }
/// <summary>
/// Returns the node type of this Expression. Extension nodes should return
/// ExpressionType.Extension when overriding this method.
/// </summary>
/// <returns>The <see cref="ExpressionType"/> of the expression.</returns>
public sealed override ExpressionType NodeType => ExpressionType.Default;
/// <summary>
/// Dispatches to the specific visit method for this node type.
/// </summary>
protected internal override Expression Accept(ExpressionVisitor visitor)
{
return visitor.VisitDefault(this);
}
}
public partial class Expression
{
/// <summary>
/// Creates an empty expression that has <see cref="Void"/> type.
/// </summary>
/// <returns>
/// A <see cref="DefaultExpression"/> that has the <see cref="NodeType"/> property equal to
/// <see cref="ExpressionType.Default"/> and the <see cref="Type"/> property set to <see cref="Void"/>.
/// </returns>
public static DefaultExpression Empty()
{
return new DefaultExpression(typeof(void)); // Create new object each time for different identity
}
/// <summary>
/// Creates a <see cref="DefaultExpression"/> that has the <see cref="Type"/> property set to the specified type.
/// </summary>
/// <param name="type">A <see cref="Type"/> to set the <see cref="Type"/> property equal to.</param>
/// <returns>
/// A <see cref="DefaultExpression"/> that has the <see cref="NodeType"/> property equal to
/// <see cref="ExpressionType.Default"/> and the <see cref="Type"/> property set to the specified type.
/// </returns>
public static DefaultExpression Default(Type type)
{
ArgumentNullException.ThrowIfNull(type);
TypeUtils.ValidateType(type, nameof(type));
return new DefaultExpression(type);
}
}
}
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