Expression.Label Method

Definition

Namespace:

System.Linq.Expressions

Assemblies:

netstandard.dll, System.Linq.Expressions.dll

Creates a LabelTarget representing a label.

Overloads

Label()	Creates a LabelTarget representing a label with void type and no name.
Label(LabelTarget)	Creates a LabelExpression representing a label without a default value.
Label(String)	Creates a LabelTarget representing a label with void type and the given name.
Label(Type)	Creates a LabelTarget representing a label with the given type.
Label(LabelTarget, Expression)	Creates a LabelExpression representing a label with the given default value.
Label(Type, String)	Creates a LabelTarget representing a label with the given type and name.

Label()

Source:

LabelTarget.cs

Creates a LabelTarget representing a label with void type and no name.

C#

public static System.Linq.Expressions.LabelTarget Label();

Returns

LabelTarget

The new LabelTarget.

Examples

The following example demonstrates how to create an expression that contains a LabelTarget object.

C#

// 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).

Label(LabelTarget)

Source:

LabelExpression.cs

Creates a LabelExpression representing a label without a default value.

C#

public static System.Linq.Expressions.LabelExpression Label(System.Linq.Expressions.LabelTarget target);

Parameters

target

LabelTarget

The LabelTarget which this LabelExpression will be associated with.

Returns

LabelExpression

A LabelExpression without a default value.

Label(String)

Source:

LabelTarget.cs

Creates a LabelTarget representing a label with void type and the given name.

C#

public static System.Linq.Expressions.LabelTarget Label(string? name);

Parameters

name

String

The name of the label.

Returns

LabelTarget

The new LabelTarget.

Label(Type)

Source:

LabelTarget.cs

Creates a LabelTarget representing a label with the given type.

C#

public static System.Linq.Expressions.LabelTarget Label(Type type);

Parameters

type

Type

The type of value that is passed when jumping to the label.

Returns

LabelTarget

The new LabelTarget.

Examples

The following example demonstrates how to use a LabelTarget object in a loop expression.

C#

// 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

Label(LabelTarget, Expression)

Source:

LabelExpression.cs

Creates a LabelExpression representing a label with the given default value.

C#

public static System.Linq.Expressions.LabelExpression Label(System.Linq.Expressions.LabelTarget target, System.Linq.Expressions.Expression? defaultValue);

Parameters

target

LabelTarget

The LabelTarget which this LabelExpression will be associated with.

defaultValue

Expression

The value of this LabelExpression when the label is reached through regular control flow.

Returns

LabelExpression

A LabelExpression with the given default value.

Label(Type, String)

Source:

LabelTarget.cs

Creates a LabelTarget representing a label with the given type and name.

C#

public static System.Linq.Expressions.LabelTarget Label(Type type, string? name);

Parameters

type

Type

The type of value that is passed when jumping to the label.

name

String

The name of the label.

Returns

LabelTarget

The new LabelTarget.