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81 lines
2.9 KiB
81 lines
2.9 KiB
5 years ago
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#if NET20 || NET30 || !NET_4_6
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// Copyright (c) Microsoft. All rights reserved.
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// Licensed under the MIT license. See LICENSE file in the project root for full license information.
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using System.Diagnostics;
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namespace System.Linq.Expressions.Reimplement
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{
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/// <summary>
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/// Represents the default value of a type or an empty expression.
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/// </summary>
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[DebuggerTypeProxy(typeof(DefaultExpressionProxy))]
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public sealed class DefaultExpression : Expression
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{
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private readonly Type _type;
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internal DefaultExpression(Type type)
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{
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_type = type;
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}
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/// <summary>
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/// Gets the static type of the expression that this <see cref="Expression" /> represents.
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/// </summary>
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/// <returns>The <see cref="Type"/> that represents the static type of the expression.</returns>
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public override Type Type
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{
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get { return _type; }
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}
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/// <summary>
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/// Returns the node type of this Expression. Extension nodes should return
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/// ExpressionType.Extension when overriding this method.
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/// </summary>
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/// <returns>The <see cref="ExpressionType"/> of the expression.</returns>
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public override ExpressionType NodeType
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{
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get { return ExpressionType.Default; }
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}
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protected internal override Expression Accept(ExpressionVisitor visitor)
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{
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return visitor.VisitDefault(this);
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}
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}
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public partial class Expression
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{
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/// <summary>
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/// Creates an empty expression that has <see cref="System.Void"/> type.
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/// </summary>
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/// <returns>
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/// A <see cref="DefaultExpression"/> that has the <see cref="P:Expression.NodeType"/> property equal to
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/// <see cref="F:ExpressionType.Default"/> and the <see cref="P:Expression.Type"/> property set to <see cref="System.Void"/>.
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/// </returns>
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public static DefaultExpression Empty()
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{
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return new DefaultExpression(typeof(void));
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}
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/// <summary>
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/// Creates a <see cref="DefaultExpression"/> that has the <see cref="P:Expression.Type"/> property set to the specified type.
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/// </summary>
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/// <param name="type">A <see cref="System.Type"/> to set the <see cref="P:Expression.Type"/> property equal to.</param>
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/// <returns>
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/// A <see cref="DefaultExpression"/> that has the <see cref="P:Expression.NodeType"/> property equal to
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/// <see cref="F:ExpressionType.Default"/> and the <see cref="P:Expression.Type"/> property set to the specified type.
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/// </returns>
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public static DefaultExpression Default(Type type)
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{
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if (type == typeof(void))
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{
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return Empty();
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}
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return new DefaultExpression(type);
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}
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}
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}
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#endif
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