Expression.Label Metodo
Definizione
Importante
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Crea un oggetto LabelTarget che rappresenta un'etichetta.
Overload
Label() |
Crea un oggetto LabelTarget che rappresenta un'etichetta con tipo void e nessun nome. |
Label(LabelTarget) |
Crea un oggetto LabelExpression che rappresenta un'etichetta senza un valore predefinito. |
Label(String) |
Crea un oggetto LabelTarget che rappresenta un'etichetta con tipo void e il nome specificato. |
Label(Type) |
Crea un oggetto LabelTarget che rappresenta un'etichetta con il tipo specificato. |
Label(LabelTarget, Expression) |
Crea un oggetto LabelExpression che rappresenta un'etichetta con il valore predefinito specificato. |
Label(Type, String) |
Crea un oggetto LabelTarget che rappresenta un'etichetta con il tipo e il nome specificati. |
Label()
- Origine:
- LabelTarget.cs
- Origine:
- LabelTarget.cs
- Origine:
- LabelTarget.cs
Crea un oggetto LabelTarget che rappresenta un'etichetta con tipo void e nessun nome.
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
Restituisce
Nuovo oggetto LabelTarget.
Esempio
Nell'esempio seguente viene illustrato come creare un'espressione contenente un LabelTarget oggetto .
// 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).
Si applica a
Label(LabelTarget)
- Origine:
- LabelExpression.cs
- Origine:
- LabelExpression.cs
- Origine:
- LabelExpression.cs
Crea un oggetto LabelExpression che rappresenta un'etichetta senza un valore predefinito.
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
Parametri
- target
- LabelTarget
Oggetto LabelTarget al quale verrà associato questo oggetto LabelExpression.
Restituisce
Oggetto LabelExpression senza un valore predefinito.
Si applica a
Label(String)
- Origine:
- LabelTarget.cs
- Origine:
- LabelTarget.cs
- Origine:
- LabelTarget.cs
Crea un oggetto LabelTarget che rappresenta un'etichetta con tipo void e il nome specificato.
public:
static System::Linq::Expressions::LabelTarget ^ Label(System::String ^ name);
public static System.Linq.Expressions.LabelTarget Label (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
Parametri
- name
- String
Nome dell'etichetta.
Restituisce
Nuovo oggetto LabelTarget.
Si applica a
Label(Type)
- Origine:
- LabelTarget.cs
- Origine:
- LabelTarget.cs
- Origine:
- LabelTarget.cs
Crea un oggetto LabelTarget che rappresenta un'etichetta con il tipo specificato.
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
Parametri
- type
- Type
Tipo di valore passato durante il passaggio all'etichetta.
Restituisce
Nuovo oggetto LabelTarget.
Esempio
Nell'esempio seguente viene illustrato come usare un LabelTarget oggetto in un'espressione ciclo.
// 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
Si applica a
Label(LabelTarget, Expression)
- Origine:
- LabelExpression.cs
- Origine:
- LabelExpression.cs
- Origine:
- LabelExpression.cs
Crea un oggetto LabelExpression che rappresenta un'etichetta con il valore predefinito specificato.
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);
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
Parametri
- target
- LabelTarget
Oggetto LabelTarget al quale verrà associato questo oggetto LabelExpression.
- defaultValue
- Expression
Valore di questo oggetto LabelExpression quando l'etichetta viene raggiunta tramite il normale flusso di controllo.
Restituisce
Oggetto LabelExpression con il valore predefinito specificato.
Si applica a
Label(Type, String)
- Origine:
- LabelTarget.cs
- Origine:
- LabelTarget.cs
- Origine:
- LabelTarget.cs
Crea un oggetto LabelTarget che rappresenta un'etichetta con il tipo e il nome specificati.
public:
static System::Linq::Expressions::LabelTarget ^ Label(Type ^ type, System::String ^ name);
public static System.Linq.Expressions.LabelTarget Label (Type type, 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
Parametri
- type
- Type
Tipo di valore passato durante il passaggio all'etichetta.
- name
- String
Nome dell'etichetta.
Restituisce
Nuovo oggetto LabelTarget.