Expression.Label メソッド

定義

名前空間:

System.Linq.Expressions

アセンブリ:

System.Linq.Expressions.dll

ラベルを表す LabelTarget を作成します。

オーバーロード

Label()	void 型で名前なしのラベルを表す LabelTarget を作成します。
Label(LabelTarget)	既定値のないラベルを表す LabelExpression を作成します。
Label(String)	指定された名前を持つ void 型のラベルを表す LabelTarget を作成します。
Label(Type)	型を指定して、ラベルを表す LabelTarget を作成します。
Label(LabelTarget, Expression)	指定された既定値を持つラベルを表す LabelExpression を作成します。
Label(Type, String)	指定した型および名前を使用して、ラベルを表す LabelTarget を作成します。

Label()

ソース:

LabelTarget.cs

void 型で名前なしのラベルを表す LabelTarget を作成します。

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

戻り値

LabelTarget

新しい LabelTarget。

例

次の例では、 オブジェクトを含む式を作成する方法を LabelTarget 示します。

// 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)

ソース:

LabelExpression.cs

既定値のないラベルを表す LabelExpression を作成します。

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

パラメーター

target

LabelTarget

この LabelTarget が関連付けられる LabelExpression。

戻り値

LabelExpression

既定値のない LabelExpression。

Label(String)

ソース:

LabelTarget.cs

指定された名前を持つ void 型のラベルを表す LabelTarget を作成します。

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

パラメーター

name

String

ラベルの名前。

戻り値

LabelTarget

新しい LabelTarget。

Label(Type)

ソース:

LabelTarget.cs

型を指定して、ラベルを表す LabelTarget を作成します。

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

パラメーター

type

Type

ラベルにジャンプするときに渡す値の型。

戻り値

LabelTarget

新しい LabelTarget。

例

次の例では、ループ式で オブジェクトを LabelTarget 使用する方法を示します。

// 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)

ソース:

LabelExpression.cs

指定された既定値を持つラベルを表す LabelExpression を作成します。

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

パラメーター

target

LabelTarget

この LabelTarget が関連付けられる LabelExpression。

defaultValue

Expression

通常の制御フローを経てラベルに到達した場合のこの LabelExpression の値。

戻り値

LabelExpression

指定された既定値を持つ LabelExpression。

Label(Type, String)

ソース:

LabelTarget.cs

指定した型および名前を使用して、ラベルを表す LabelTarget を作成します。

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

パラメーター

type

Type

ラベルにジャンプするときに渡す値の型。

name

String

ラベルの名前。

戻り値

LabelTarget

新しい LabelTarget。