Статья
11/18/2011

Expression.Return Method (LabelTarget, Expression)

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

Creates a GotoExpression representing a return statement. The value passed to the label upon jumping can be specified.

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

Syntax

'Declaration
Public Shared Function Return ( _
    target As LabelTarget, _
    value As Expression _
) As GotoExpression

public static GotoExpression Return(
    LabelTarget target,
    Expression value
)

Parameters

target
Type: System.Linq.Expressions.LabelTarget
The LabelTarget that the GotoExpression will jump to.

value
Type: System.Linq.Expressions.Expression
The value that will be passed to the associated label upon jumping.

Return Value

Type: System.Linq.Expressions.GotoExpression
A GotoExpression with Kind equal to Continue, the Target property set to target, and value to be passed to the target label upon jumping.

Examples

The following example demonstrates how to create an expression that contains the Return method.

' Add the following directive to the file:
' Imports System.Linq.Expressions  
' A label expression of the void type that is the target for Expression.Return().
Dim returnTarget As LabelTarget = Expression.Label()

' This block contains a GotoExpression that represents a return statement with no value.
' It transfers execution to a label expression that is initialized with the same LabelTarget as the GotoExpression.
' The types of the GotoExpression, label expression, and LabelTarget must match.
Dim blockExpr As BlockExpression =
      Expression.Block(
          Expression.Call(GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}), Expression.Constant("Return")),
          Expression.Return(returnTarget),
          Expression.Call(GetType(Console).GetMethod("WriteLine", New Type() {GetType(String)}), Expression.Constant("Other Work")),
          Expression.Label(returnTarget)
      )

' The following statement first creates an expression tree,
' then compiles it, and then runs it.
Expression.Lambda(Of Action)(blockExpr).Compile()()

' This code example produces the following output:
'
' Return

' "Other Work" is not printed because 
' the Return expression transfers execution from Return(returnTarget)
' to Expression.Label(returnTarget).

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

// A label expression of the void type that is the target for Expression.Return().
LabelTarget returnTarget = Expression.Label();

// This block contains a GotoExpression that represents a return statement with no value.
// It transfers execution to a label expression that is initialized with the same LabelTarget as the GotoExpression.
// The types of the GotoExpression, label expression, and LabelTarget must match.
BlockExpression blockExpr =
    Expression.Block(
        Expression.Call(typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }), Expression.Constant("Return")),
        Expression.Return(returnTarget),
        Expression.Call(typeof(Console).GetMethod("WriteLine", new Type[] { typeof(string) }), Expression.Constant("Other Work")),
        Expression.Label(returnTarget)
    );

// The following statement first creates an expression tree,
// then compiles it, and then runs it.
Expression.Lambda<Action>(blockExpr).Compile()();

// This code example produces the following output:
//
// Return

// "Other Work" is not printed because 
// the Return expression transfers execution from Expression.Return(returnTarget)
// to Expression.Label(returnTarget).

Version Information

Silverlight

Supported in: 5, 4

Platforms

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

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