Článek
11/18/2011

LambdaExpression Class

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

Describes a lambda expression. This captures a block of code that is similar to a .NET method body.

Inheritance Hierarchy

System.Object
  System.Linq.Expressions.Expression
    System.Linq.Expressions.LambdaExpression
      System.Linq.Expressions.Expression<TDelegate>

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

Syntax

'Declaration
Public MustInherit Class LambdaExpression _
    Inherits Expression

public abstract class LambdaExpression : Expression

The LambdaExpression type exposes the following members.

Properties

	Name	Description
	Body	Gets the body of the lambda expression.
	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.)
	Name	Gets the name of the lambda expression.
	NodeType	Returns the node type of this Expression. (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.
	Parameters	Gets the parameters of the lambda expression.
	ReturnType	Gets the return type of the lambda expression.
	TailCall	Gets the value that indicates if the lambda expression will be compiled with the tail call optimization.
	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.

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Methods

	Name	Description
	Accept	Dispatches to the specific visit method for this node type. For example, MethodCallExpression calls the VisitMethodCall. (Inherited from Expression.)
	Compile()	Produces a delegate that represents the lambda expression.
	Compile(DebugInfoGenerator)	Produces a delegate that represents the lambda expression.
	CompileToMethod(MethodBuilder)	Compiles the lambda into a method definition.
	CompileToMethod(MethodBuilder, DebugInfoGenerator)	Compiles the lambda into a method definition and custom debug information.
	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

The LambdaExpression type represents a lambda expression in the form of an expression tree. The Expression<TDelegate> type, which derives from LambdaExpression and captures the type of the lambda expression more explicitly, can also be used to represent a lambda expression. At runtime, an expression tree node that represents a lambda expression is always of type Expression<TDelegate>.

The value of the NodeType property of a LambdaExpression is Lambda.

Use the Lambda factory methods to create a LambdaExpression object.

Examples

The following example demonstrates how to create an expression that represents a lambda expression that adds 1 to the passed argument by using the Lambda method.

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

' A parameter for the lambda expression.
Dim paramExpr As ParameterExpression = Expression.Parameter(GetType(Integer), "arg")

' This expression represents a lambda expression
' that adds 1 to the parameter value.
Dim lambdaExpr As LambdaExpression = Expression.Lambda(
        Expression.Add(
            paramExpr,
            Expression.Constant(1)
        ),
        New List(Of ParameterExpression)() From {paramExpr}
    )

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

' Compile and run the lamda expression.
' The value of the parameter is 1.
outputBlock.Text &= lambdaExpr.Compile().DynamicInvoke(1).ToString() & vbCrLf

' This code example produces the following output:
'
' arg => (arg +1)
' 2

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

// A parameter for the lambda expression.
ParameterExpression paramExpr = Expression.Parameter(typeof(int), "arg");

// This expression represents a lambda expression
// that adds 1 to the parameter value.
LambdaExpression lambdaExpr = Expression.Lambda(
    Expression.Add(
        paramExpr,
        Expression.Constant(1)
    ),
    new List<ParameterExpression>() { paramExpr }
);

// Print out the expression.
outputBlock.Text += lambdaExpr + "\n";

// Compile and run the lamda expression.
// The value of the parameter is 1.
outputBlock.Text += lambdaExpr.Compile().DynamicInvoke(1) + "\n";

// This code example produces the following output:
//
// arg => (arg +1)
// 2

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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