Expression.Label Méthode

Définition

Crée un LabelTarget représentant une étiquette.Creates a LabelTarget representing a label.

Surcharges

Label()

Crée un LabelTarget qui représente une étiquette avec le type void et aucun nom.Creates a LabelTarget representing a label with void type and no name.

Label(LabelTarget)

Crée un LabelExpression qui représente une étiquette sans valeur par défaut.Creates a LabelExpression representing a label without a default value.

Label(String)

Crée un LabelTarget représentant une étiquette avec le type void et le nom donné.Creates a LabelTarget representing a label with void type and the given name.

Label(Type)

Crée un LabelTarget représentant une étiquette avec le type donné.Creates a LabelTarget representing a label with the given type.

Label(LabelTarget, Expression)

Crée un LabelExpression qui représente une étiquette avec la valeur par défaut donnée.Creates a LabelExpression representing a label with the given default value.

Label(Type, String)

Crée un LabelTarget qui représente une étiquette avec le type et le nom donnés.Creates a LabelTarget representing a label with the given type and name.

Label()

Crée un LabelTarget qui représente une étiquette avec le type void et aucun nom.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

Retours

Nouvelle LabelTarget.The new LabelTarget.

Exemples

L’exemple suivant montre comment créer une expression qui contient un LabelTarget objet.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)

Crée un LabelExpression qui représente une étiquette sans valeur par défaut.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

Paramètres

target
LabelTarget

LabelTarget auquel LabelExpression sera associé.The LabelTarget which this LabelExpression will be associated with.

Retours

LabelExpression sans valeur par défaut.A LabelExpression without a default value.

Label(String)

Crée un LabelTarget représentant une étiquette avec le type void et le nom donné.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

Paramètres

name
String

Nom de l'étiquette.The name of the label.

Retours

Nouvelle LabelTarget.The new LabelTarget.

Label(Type)

Crée un LabelTarget représentant une étiquette avec le type donné.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

Paramètres

type
Type

Type de valeur passée lors de l'accès à l'étiquette.The type of value that is passed when jumping to the label.

Retours

Nouvelle LabelTarget.The new LabelTarget.

Exemples

L’exemple suivant montre comment utiliser un LabelTarget objet dans une expression de boucle.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)

Crée un LabelExpression qui représente une étiquette avec la valeur par défaut donnée.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

Paramètres

target
LabelTarget

LabelTarget auquel LabelExpression sera associé.The LabelTarget which this LabelExpression will be associated with.

defaultValue
Expression

Valeur de ce LabelExpression lorsque l'étiquette est atteinte via un flux de contrôle normal.The value of this LabelExpression when the label is reached through regular control flow.

Retours

LabelExpression avec la valeur par défaut donnée.A LabelExpression with the given default value.

Label(Type, String)

Crée un LabelTarget qui représente une étiquette avec le type et le nom donnés.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

Paramètres

type
Type

Type de valeur passée lors de l'accès à l'étiquette.The type of value that is passed when jumping to the label.

name
String

Nom de l'étiquette.The name of the label.

Retours

Nouvelle LabelTarget.The new LabelTarget.

S’applique à