Expression.Label Metode

Definisi

Ruang nama:

System.Linq.Expressions

Rakitan:

System.Linq.Expressions.dll

LabelTarget Membuat yang mewakili label.

Overload

Label()	LabelTarget Membuat yang mewakili label dengan jenis kekosongan dan tanpa nama.
Label(LabelTarget)	LabelExpression Membuat yang mewakili label tanpa nilai default.
Label(String)	LabelTarget Membuat yang mewakili label dengan jenis kekosongan dan nama yang diberikan.
Label(Type)	LabelTarget Membuat yang mewakili label dengan jenis yang diberikan.
Label(LabelTarget, Expression)	LabelExpression Membuat yang mewakili label dengan nilai default yang diberikan.
Label(Type, String)	LabelTarget Membuat yang mewakili label dengan jenis dan nama yang diberikan.

Label()

Sumber:

LabelTarget.cs

LabelTarget Membuat yang mewakili label dengan jenis kekosongan dan tanpa nama.

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

Mengembalikan

LabelTarget

Yang baru LabelTarget.

Contoh

Contoh berikut menunjukkan cara membuat ekspresi yang berisi LabelTarget objek .

// 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)

Sumber:

LabelExpression.cs

LabelExpression Membuat yang mewakili label tanpa nilai default.

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

Parameter

target

LabelTarget

Yang LabelTarget akan dikaitkan dengan ini LabelExpression .

Mengembalikan

LabelExpression

A LabelExpression tanpa nilai default.

Label(String)

Sumber:

LabelTarget.cs

LabelTarget Membuat yang mewakili label dengan jenis kekosongan dan nama yang diberikan.

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

Parameter

name

String

Nama label.

Mengembalikan

LabelTarget

Yang baru LabelTarget.

Label(Type)

Sumber:

LabelTarget.cs

LabelTarget Membuat yang mewakili label dengan jenis yang diberikan.

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

Parameter

type

Type

Jenis nilai yang diteruskan saat melompat ke label.

Mengembalikan

LabelTarget

Yang baru LabelTarget.

Contoh

Contoh berikut menunjukkan cara menggunakan LabelTarget objek dalam ekspresi perulangan.

// 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)

Sumber:

LabelExpression.cs

LabelExpression Membuat yang mewakili label dengan nilai default yang diberikan.

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

Parameter

target

LabelTarget

Yang LabelTarget akan dikaitkan dengan ini LabelExpression .

defaultValue

Expression

Nilai ini LabelExpression ketika label tercapai melalui alur kontrol reguler.

Mengembalikan

LabelExpression

A LabelExpression dengan nilai default yang diberikan.

Label(Type, String)

Sumber:

LabelTarget.cs

LabelTarget Membuat yang mewakili label dengan jenis dan nama yang diberikan.

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

Parameter

type

Type

Jenis nilai yang diteruskan saat melompat ke label.

name

String

Nama label.

Mengembalikan

LabelTarget

Yang baru LabelTarget.