Artikel
11/18/2011

ConstantExpression Class

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Represents an expression that has a constant value.

Inheritance Hierarchy

System.Object
System.Linq.Expressions.Expression
System.Linq.Expressions.ConstantExpression

Namespace: System.Linq.Expressions
Assembly: System.Core (in System.Core.dll)

Syntax

'Declaration
Public Class ConstantExpression _
    Inherits Expression

public class ConstantExpression : Expression

The ConstantExpression type exposes the following members.

Properties

	Name	Description
	CanReduce	Indicates that the node can be reduced to a simpler node. If this returns true, Reduce() can be called to produce the reduced form. (Inherited from Expression.)
	NodeType	Returns the node type of this Expression. Extension nodes should return Extension when overriding this method. (Overrides Expression.NodeType.) In Silverlight for Windows Phone Windows Phone OS 7.1, this member is inherited from Expression.NodeType. In XNA Framework Windows Phone OS 7.0, this member is inherited from Expression.NodeType.
	Type	Gets the static type of the expression that this Expression represents. (Overrides Expression.Type.) In Silverlight for Windows Phone Windows Phone OS 7.1, this member is inherited from Expression.Type. In XNA Framework Windows Phone OS 7.0, this member is inherited from Expression.Type.
	Value	Gets the value of the constant expression.

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Methods

	Name	Description
	Accept	Dispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall. (Overrides Expression.Accept(ExpressionVisitor).)
	Equals(Object)	Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
	Finalize	Allows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
	GetHashCode	Serves as a hash function for a particular type. (Inherited from Object.)
	GetType	Gets the Type of the current instance. (Inherited from Object.)
	MemberwiseClone	Creates a shallow copy of the current Object. (Inherited from Object.)
	Reduce	Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression.)
	ReduceAndCheck	Reduces this node to a simpler expression. If CanReduce returns true, this should return a valid expression. This method can return another node which itself must be reduced. (Inherited from Expression.)
	ReduceExtensions	Reduces the expression to a known node type (that is not an Extension node) or just returns the expression if it is already a known type. (Inherited from Expression.)
	ToString	Returns a textual representation of the Expression. (Inherited from Expression.)
	VisitChildren	Reduces the node and then calls the visitor delegate on the reduced expression. The method throws an exception if the node is not reducible. (Inherited from Expression.)

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Remarks

Use the Constant factory methods to create a ConstantExpression.

The NodeType of a ConstantExpression is Constant.

Examples

The following code example shows how to create an expression that represents a constant value by using the Constant method.

' Add the following directive to your file:
' Imports System.Linq.Expressions 

' This expression represents a constant value.
Dim constantExpr As Expression = Expression.Constant(5.5)

' Print the expression.
outputBlock.Text &= constantExpr.ToString() & vbCrLf

' You can also use variables.
Dim num As Double = 3.5
constantExpr = Expression.Constant(num)
outputBlock.Text &= constantExpr.ToString() & vbCrLf

' This code example produces the following output:
'
' 5.5
' 3.5

// Add the following directive to your file:
// using System.Linq.Expressions;  

// This expression represents a Constant value.
Expression constantExpr = Expression.Constant(5.5);

// Print out the expression.
outputBlock.Text += constantExpr.ToString() + "\n";

// You can also use variables.
double num = 3.5;
constantExpr = Expression.Constant(num);
outputBlock.Text += constantExpr.ToString() + "\n";

// This code example produces the following output:
//
// 5.5
// 3.5

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Thread Safety

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

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