Expression.Label Метод

Определение

Создает объект LabelTarget, представляющий метку.Creates a LabelTarget representing a label.

Перегрузки

Label()

Создает объект LabelTarget, представляющий метку с типом void, не имеющую имени.Creates a LabelTarget representing a label with void type and no name.

Label(LabelTarget)

Создает объект LabelExpression, представляющий метку без значения по умолчанию.Creates a LabelExpression representing a label without a default value.

Label(String)

Создает объектLabelTarget, представляющий метку с типом void и заданным именем.Creates a LabelTarget representing a label with void type and the given name.

Label(Type)

Создает объект LabelTarget, представляющий метку с заданным типом.Creates a LabelTarget representing a label with the given type.

Label(LabelTarget, Expression)

Создает выражение LabelExpression, представляющее метку с заданным значением по умолчанию.Creates a LabelExpression representing a label with the given default value.

Label(Type, String)

Создает объект LabelTarget, представляющий метку с заданными типом и именем.Creates a LabelTarget representing a label with the given type and name.

Label()

Создает объект LabelTarget, представляющий метку с типом void, не имеющую имени.Creates a LabelTarget representing a label with void type and no name.

public:
 static System::Linq::Expressions::LabelTarget ^ Label();
public static System.Linq.Expressions.LabelTarget Label ();
static member Label : unit -> System.Linq.Expressions.LabelTarget
Public Shared Function Label () As LabelTarget

Возвраты

Новый объект LabelTarget.The new LabelTarget.

Примеры

В следующем примере показано, как создать выражение, содержащее LabelTarget объект.The following example demonstrates how to create an expression that contains a LabelTarget object.

// 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).
' 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).

Label(LabelTarget)

Создает объект LabelExpression, представляющий метку без значения по умолчанию.Creates a LabelExpression representing a label without a default value.

public:
 static System::Linq::Expressions::LabelExpression ^ Label(System::Linq::Expressions::LabelTarget ^ target);
public static System.Linq.Expressions.LabelExpression Label (System.Linq.Expressions.LabelTarget target);
static member Label : System.Linq.Expressions.LabelTarget -> System.Linq.Expressions.LabelExpression
Public Shared Function Label (target As LabelTarget) As LabelExpression

Параметры

target
LabelTarget

Объект LabelTarget, с которым будет связано данное выражение LabelExpression.The LabelTarget which this LabelExpression will be associated with.

Возвраты

LabelExpression без значения по умолчанию.A LabelExpression without a default value.

Label(String)

Создает объектLabelTarget, представляющий метку с типом void и заданным именем.Creates a LabelTarget representing a label with void type and the given name.

public:
 static System::Linq::Expressions::LabelTarget ^ Label(System::String ^ name);
public static System.Linq.Expressions.LabelTarget Label (string name);
static member Label : string -> System.Linq.Expressions.LabelTarget
Public Shared Function Label (name As String) As LabelTarget

Параметры

name
String

Имя метки.The name of the label.

Возвраты

Новый объект LabelTarget.The new LabelTarget.

Label(Type)

Создает объект LabelTarget, представляющий метку с заданным типом.Creates a LabelTarget representing a label with the given type.

public:
 static System::Linq::Expressions::LabelTarget ^ Label(Type ^ type);
public static System.Linq.Expressions.LabelTarget Label (Type type);
static member Label : Type -> System.Linq.Expressions.LabelTarget

Параметры

type
Type

Тип значения, которое передается при переходе к метке.The type of value that is passed when jumping to the label.

Возвраты

Новый объект LabelTarget.The new LabelTarget.

Примеры

В следующем примере показано, как использовать LabelTarget объект в выражении цикла.The following example demonstrates how to use a LabelTarget object in a loop expression.

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

// Creating a parameter expression.
ParameterExpression value = Expression.Parameter(typeof(int), "value");

// Creating an expression to hold a local variable. 
ParameterExpression result = Expression.Parameter(typeof(int), "result");

// Creating a label to jump to from a loop.
LabelTarget label = Expression.Label(typeof(int));

// Creating a method body.
BlockExpression block = Expression.Block(
    new[] { result },
    Expression.Assign(result, Expression.Constant(1)),
        Expression.Loop(
           Expression.IfThenElse(
               Expression.GreaterThan(value, Expression.Constant(1)),
               Expression.MultiplyAssign(result,
                   Expression.PostDecrementAssign(value)),
               Expression.Break(label, result)
           ),
       label
    )
);

// Compile and run an expression tree.
int factorial = Expression.Lambda<Func<int, int>>(block, value).Compile()(5);

Console.WriteLine(factorial);

// This code example produces the following output:
//
// 120
' Add the following directive to the file:
' Imports System.Linq.Expressions  

' Creating a parameter expression.
Dim value As ParameterExpression =
    Expression.Parameter(GetType(Integer), "value")

' Creating an expression to hold a local variable. 
Dim result As ParameterExpression =
    Expression.Parameter(GetType(Integer), "result")

' Creating a label to jump to from a loop.
Dim label As LabelTarget = Expression.Label(GetType(Integer))

' Creating a method body.
Dim block As BlockExpression = Expression.Block(
    New ParameterExpression() {result},
    Expression.Assign(result, Expression.Constant(1)),
    Expression.Loop(
        Expression.IfThenElse(
            Expression.GreaterThan(value, Expression.Constant(1)),
            Expression.MultiplyAssign(result,
                Expression.PostDecrementAssign(value)),
            Expression.Break(label, result)
        ),
        label
    )
)

' Compile an expression tree and return a delegate.
Dim factorial As Integer =
    Expression.Lambda(Of Func(Of Integer, Integer))(block, value).Compile()(5)

Console.WriteLine(factorial)

' This code example produces the following output:
'
' 120

Label(LabelTarget, Expression)

Создает выражение LabelExpression, представляющее метку с заданным значением по умолчанию.Creates a LabelExpression representing a label with the given default value.

public:
 static System::Linq::Expressions::LabelExpression ^ Label(System::Linq::Expressions::LabelTarget ^ target, System::Linq::Expressions::Expression ^ defaultValue);
public static System.Linq.Expressions.LabelExpression Label (System.Linq.Expressions.LabelTarget target, System.Linq.Expressions.Expression defaultValue);
static member Label : System.Linq.Expressions.LabelTarget * System.Linq.Expressions.Expression -> System.Linq.Expressions.LabelExpression
Public Shared Function Label (target As LabelTarget, defaultValue As Expression) As LabelExpression

Параметры

target
LabelTarget

Объект LabelTarget, с которым будет связано данное выражение LabelExpression.The LabelTarget which this LabelExpression will be associated with.

defaultValue
Expression

Значение данного выражения LabelExpression после достижения метки через стандартный поток управления.The value of this LabelExpression when the label is reached through regular control flow.

Возвраты

LabelExpression с заданным значением по умолчанию.A LabelExpression with the given default value.

Label(Type, String)

Создает объект LabelTarget, представляющий метку с заданными типом и именем.Creates a LabelTarget representing a label with the given type and name.

public:
 static System::Linq::Expressions::LabelTarget ^ Label(Type ^ type, System::String ^ name);
public static System.Linq.Expressions.LabelTarget Label (Type type, string name);
static member Label : Type * string -> System.Linq.Expressions.LabelTarget

Параметры

type
Type

Тип значения, которое передается при переходе к метке.The type of value that is passed when jumping to the label.

name
String

Имя метки.The name of the label.

Возвраты

Новый объект LabelTarget.The new LabelTarget.

Применяется к