Expression.Label Metoda

Definicja

Przestrzeń nazw:

System.Linq.Expressions

Zestaw:

System.Linq.Expressions.dll

Tworzy etykietę LabelTarget reprezentującą.

Przeciążenia

Label()	Tworzy etykietę LabelTarget reprezentującą z typem pustki i bez nazwy.
Label(LabelTarget)	Tworzy etykietę LabelExpression reprezentującą bez wartości domyślnej.
Label(String)	Tworzy reprezentującą etykietę LabelTarget o typie pustki i podanej nazwie.
Label(Type)	Tworzy etykietę LabelTarget reprezentującą dany typ.
Label(LabelTarget, Expression)	Tworzy etykietę LabelExpression reprezentującą daną wartość domyślną.
Label(Type, String)	Tworzy etykietę LabelTarget reprezentującą daną nazwę i typ.

Label()

Źródło:

LabelTarget.cs

Tworzy etykietę LabelTarget reprezentującą z typem pustki i bez nazwy.

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

Zwraca

LabelTarget

Nowy LabelTargetelement .

Przykłady

W poniższym przykładzie pokazano, jak utworzyć wyrażenie zawierające LabelTarget obiekt.

// 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)

Źródło:

LabelExpression.cs

Tworzy etykietę LabelExpression reprezentującą bez wartości domyślnej.

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

Parametry

target

LabelTarget

Z LabelTarget którymi będzie to LabelExpression skojarzone.

Zwraca

LabelExpression

Wartość LabelExpression bez wartości domyślnej.

Label(String)

Źródło:

LabelTarget.cs

Tworzy reprezentującą etykietę LabelTarget o typie pustki i podanej nazwie.

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

Parametry

name

String

Nazwa etykiety.

Zwraca

LabelTarget

Nowy LabelTargetelement .

Label(Type)

Źródło:

LabelTarget.cs

Tworzy etykietę LabelTarget reprezentującą dany typ.

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

Parametry

type

Type

Typ wartości przekazywanej podczas przechodzenia do etykiety.

Zwraca

LabelTarget

Nowy LabelTargetelement .

Przykłady

W poniższym przykładzie pokazano, jak używać LabelTarget obiektu w wyrażeniu pętli.

// 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)

Źródło:

LabelExpression.cs

Tworzy etykietę LabelExpression reprezentującą daną wartość domyślną.

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

Parametry

target

LabelTarget

Z LabelTarget którymi będzie to LabelExpression skojarzone.

defaultValue

Expression

Wartość tej LabelExpression wartości, gdy etykieta zostanie osiągnięta przez regularny przepływ sterowania.

Zwraca

LabelExpression

A LabelExpression z daną wartością domyślną.

Label(Type, String)

Źródło:

LabelTarget.cs

Tworzy etykietę LabelTarget reprezentującą daną nazwę i typ.

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

Parametry

type

Type

Typ wartości przekazywanej podczas przechodzenia do etykiety.

name

String

Nazwa etykiety.

Zwraca

LabelTarget

Nowy LabelTargetelement .