Expression.Label Método

Definición

Espacio de nombres:

System.Linq.Expressions

Ensamblado:

System.Linq.Expressions.dll

Crea un LabelTarget que representa una etiqueta.

Sobrecargas

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 un tipo void y con el nombre dado.
Label(Type)	Crea un objeto LabelTarget que representa una etiqueta con el tipo dado.
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 dados.

Label()

Source:

LabelTarget.cs

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

Nuevo objeto LabelTarget.

Ejemplos

En el ejemplo siguiente se muestra cómo crear una expresión que contiene 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).

Label(LabelTarget)

Source:

LabelExpression.cs

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

LabelTarget con el que se asociará este objeto LabelExpression.

Devoluciones

LabelExpression

Objeto LabelExpression sin un valor predeterminado.

Label(String)

Source:

LabelTarget.cs

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

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

Nuevo objeto LabelTarget.

Label(Type)

Source:

LabelTarget.cs

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

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 cuando se produce el salto a la etiqueta.

Devoluciones

LabelTarget

Nuevo objeto 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

Label(LabelTarget, Expression)

Source:

LabelExpression.cs

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

LabelTarget con el que se asociará este objeto LabelExpression.

defaultValue

Expression

Valor de este objeto LabelExpression cuando se alcanza la etiqueta mediante el flujo de control regular.

Devoluciones

LabelExpression

LabelExpression con el valor predeterminado dado.

Label(Type, String)

Source:

LabelTarget.cs

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

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 cuando se produce el salto a la etiqueta.

name

String

Nombre de la etiqueta.

Devoluciones

LabelTarget

Nuevo objeto LabelTarget.