Expression.Label Método

Definición

Espacio de nombres:: System.Linq.Expressions

Ensamblados:: System.Core.dll, System.Linq.Expressions.dll

Ensamblado:: System.Core.dll

Ensamblado:: System.Linq.Expressions.dll

Ensamblado:: netstandard.dll

Importante

Parte de la información hace referencia a la versión preliminar del producto, que puede haberse modificado sustancialmente antes de lanzar la versión definitiva. Microsoft no otorga ninguna garantía, explícita o implícita, con respecto a la información proporcionada aquí.

Crea un objeto LabelTarget que representa una etiqueta.

Sobrecargas

Nombre	Description
Label()	Crea un objeto LabelTarget que representa una etiqueta con tipo void y sin nombre.
Label(LabelTarget)	Crea un objeto LabelExpression que representa una etiqueta sin un valor predeterminado.
Label(String)	Crea un objeto LabelTarget que representa una etiqueta con tipo void y el nombre especificado.
Label(Type)	Crea un objeto LabelTarget que representa una etiqueta con el tipo especificado.
Label(LabelTarget, Expression)	Crea un objeto LabelExpression que representa una etiqueta con el valor predeterminado especificado.
Label(Type, String)	Crea un objeto LabelTarget que representa una etiqueta con el tipo y el nombre especificados.

Label()

Crea un objeto LabelTarget que representa una etiqueta con tipo void y sin nombre.

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

Devoluciones

LabelTarget

El nuevo LabelTarget.

Ejemplos

En el ejemplo siguiente se muestra cómo crear una expresión que contenga un LabelTarget objeto .

// 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).

Se aplica a

Label(LabelTarget)

Crea un objeto LabelExpression que representa una etiqueta sin un valor predeterminado.

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

Parámetros

target: LabelTarget

al LabelTarget que LabelExpression se asociará.

Devoluciones

LabelExpression

sin LabelExpression un valor predeterminado.

Se aplica a

Label(String)

Crea un objeto LabelTarget que representa una etiqueta con tipo void y el nombre especificado.

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

Parámetros

name: String

Nombre de la etiqueta.

Devoluciones

LabelTarget

El nuevo LabelTarget.

Se aplica a

Label(Type)

Crea un objeto LabelTarget que representa una etiqueta con el tipo especificado.

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

Public Shared Function Label (type As Type) As LabelTarget

Parámetros

type: Type

Tipo de valor que se pasa al saltar a la etiqueta.

Devoluciones

LabelTarget

El nuevo LabelTarget.

Ejemplos

En el ejemplo siguiente se muestra cómo usar un LabelTarget objeto en una expresión de bucle.

// 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

Se aplica a

Label(LabelTarget, Expression)

Crea un objeto LabelExpression que representa una etiqueta con el valor predeterminado especificado.

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

Parámetros

target: LabelTarget

al LabelTarget que LabelExpression se asociará.

defaultValue: Expression

Valor de esto LabelExpression cuando se alcanza la etiqueta a través del flujo de control normal.

Devoluciones

LabelExpression

con LabelExpression el valor predeterminado especificado.

Se aplica a

Label(Type, String)

Crea un objeto LabelTarget que representa una etiqueta con el tipo y el nombre especificados.

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

Public Shared Function Label (type As Type, name As String) As LabelTarget

Parámetros

type: Type

Tipo de valor que se pasa al saltar a la etiqueta.

name: String

Nombre de la etiqueta.

Devoluciones

LabelTarget

El nuevo LabelTarget.

Se aplica a

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