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/* ****************************************************************************
*
* Copyright (c) Microsoft Corporation.
*
* This source code is subject to terms and conditions of the Apache License, Version 2.0. A
* copy of the license can be found in the License.html file at the root of this distribution. If
* you cannot locate the Apache License, Version 2.0, please send an email to
* dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound
* by the terms of the Apache License, Version 2.0.
*
* You must not remove this notice, or any other, from this software.
*
*
* ***************************************************************************/
using System;
using System.Diagnostics;
using System.Dynamic.Utils;
#if SILVERLIGHT
using System.Core;
#endif
#if CLR2
namespace Microsoft.Scripting.Ast {
#else
namespace System.Linq.Expressions {
#endif
/// <summary>
/// Represents an expression that has a constant value.
/// </summary>
#if !SILVERLIGHT
[DebuggerTypeProxy(typeof(Expression.ConstantExpressionProxy))]
#endif
public class ConstantExpression : Expression {
// Possible optimization: we could have a Constant<T> subclass that
// stores the unboxed value.
private readonly object _value;
internal ConstantExpression(object value) {
_value = value;
}
internal static ConstantExpression Make(object value, Type type) {
if ((value == null && type == typeof(object)) || (value != null && value.GetType() == type)) {
return new ConstantExpression(value);
} else {
return new TypedConstantExpression(value, type);
}
}
/// <summary>
/// Gets the static type of the expression that this <see cref="Expression" /> represents.
/// </summary>
/// <returns>The <see cref="Type"/> that represents the static type of the expression.</returns>
public override Type Type {
get {
if (_value == null) {
return typeof(object);
}
return _value.GetType();
}
}
/// <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 {
get { return ExpressionType.Constant; }
}
/// <summary>
/// Gets the value of the constant expression.
/// </summary>
public object Value {
get { return _value; }
}
/// <summary>
/// Dispatches to the specific visit method for this node type.
/// </summary>
protected internal override Expression Accept(ExpressionVisitor visitor) {
return visitor.VisitConstant(this);
}
}
internal class TypedConstantExpression : ConstantExpression {
private readonly Type _type;
internal TypedConstantExpression(object value, Type type)
: base(value) {
_type = type;
}
public sealed override Type Type {
get { return _type; }
}
}
public partial class Expression {
/// <summary>
/// Creates a <see cref="ConstantExpression"/> that has the <see cref="P:ConstantExpression.Value"/> property set to the specified value. .
/// </summary>
/// <param name="value">An <see cref="System.Object"/> to set the <see cref="P:ConstantExpression.Value"/> property equal to.</param>
/// <returns>
/// A <see cref="ConstantExpression"/> that has the <see cref="P:Expression.NodeType"/> property equal to
/// <see cref="F:ExpressionType.Constant"/> and the <see cref="P:Expression.Value"/> property set to the specified value.
/// </returns>
public static ConstantExpression Constant(object value) {
return ConstantExpression.Make(value, value == null ? typeof(object) : value.GetType());
}
/// <summary>
/// Creates a <see cref="ConstantExpression"/> that has the <see cref="P:ConstantExpression.Value"/>
/// and <see cref="P:ConstantExpression.Type"/> properties set to the specified values. .
/// </summary>
/// <param name="value">An <see cref="System.Object"/> to set the <see cref="P:ConstantExpression.Value"/> property equal to.</param>
/// <param name="type">A <see cref="System.Type"/> to set the <see cref="P:Expression.Type"/> property equal to.</param>
/// <returns>
/// A <see cref="ConstantExpression"/> that has the <see cref="P:Expression.NodeType"/> property equal to
/// <see cref="F:ExpressionType.Constant"/> and the <see cref="P:ConstantExpression.Value"/> and
/// <see cref="P:Expression.Type"/> properties set to the specified values.
/// </returns>
public static ConstantExpression Constant(object value, Type type) {
ContractUtils.RequiresNotNull(type, "type");
if (value == null && type.IsValueType && !TypeUtils.IsNullableType(type)) {
throw Error.ArgumentTypesMustMatch();
}
if (value != null && !type.IsAssignableFrom(value.GetType())) {
throw Error.ArgumentTypesMustMatch();
}
return ConstantExpression.Make(value, type);
}
}
}
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