IteratorStateMachineAttribute Class

.NET Framework 4.5

Indicates whether a method in Visual Basic is marked with the Iterator modifier.

System.Object
  System.Attribute
    System.Runtime.CompilerServices.StateMachineAttribute
      System.Runtime.CompilerServices.IteratorStateMachineAttribute

Namespace:  System.Runtime.CompilerServices
Assembly:  mscorlib (in mscorlib.dll)

'Declaration
<SerializableAttribute> _
<AttributeUsageAttribute(AttributeTargets.Method, Inherited := False, AllowMultiple := False)> _
Public NotInheritable Class IteratorStateMachineAttribute _
	Inherits StateMachineAttribute

The IteratorStateMachineAttribute type exposes the following members.

  NameDescription
Public methodSupported in .NET for Windows Store appsIteratorStateMachineAttributeInitializes a new instance of the IteratorStateMachineAttribute class.
Top

  NameDescription
Public propertySupported in .NET for Windows Store appsStateMachineTypeReturns the type object for the underlying state machine type that was generated by the compiler to implement the state machine method. (Inherited from StateMachineAttribute.)
Public propertyTypeIdWhen implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute.)
Top

  NameDescription
Public methodSupported in .NET for Windows Store appsEqualsInfrastructure. Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute.)
Public methodSupported in .NET for Windows Store appsGetHashCodeReturns the hash code for this instance. (Inherited from Attribute.)
Public methodSupported in .NET for Windows Store appsGetTypeGets the Type of the current instance. (Inherited from Object.)
Public methodIsDefaultAttributeWhen overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute.)
Public methodMatchWhen overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute.)
Public methodSupported in .NET for Windows Store appsToStringReturns a string that represents the current object. (Inherited from Object.)
Top

  NameDescription
Explicit interface implemetationPrivate method_Attribute.GetIDsOfNamesMaps a set of names to a corresponding set of dispatch identifiers. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoRetrieves the type information for an object, which can be used to get the type information for an interface. (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.GetTypeInfoCountRetrieves the number of type information interfaces that an object provides (either 0 or 1). (Inherited from Attribute.)
Explicit interface implemetationPrivate method_Attribute.InvokeProvides access to properties and methods exposed by an object. (Inherited from Attribute.)
Top

You shouldn't apply the IteratorStateMachine attribute to methods in your code. For methods in Visual Basic that have the Iterator (Visual Basic) modifier, the compiler will apply the IteratorStateMachine attribute in the IL that it emits.

When a method (MethodName) in Visual Basic has the Iterator modifier, the compiler emits IL that includes a state machine structure. That structure contains the code in the method. That IL also contains a stub method (MethodName) that calls into the state machine. The compiler adds the IteratorStateMachine attribute to the stub method so that tools can identify the corresponding state machine. Details of the emitted IL might change in future releases of the compilers.

An iterator method performs a custom iteration over a collection by using the Yield (Visual Basic) statement to return each element one at a time. For more information, see Iterators (C# and Visual Basic).

NoteNote

You can't use IteratorStateMachineAttribute to test whether a method is an iterator method in C#.

The following example shows how to determine whether a method is an iterator method. In the example, IsIteratorMethod performs the following steps:

  • Obtains a MethodInfo object for the method name by using Type.GetMethod.

  • Obtains a Type object for the attribute by using GetType Operator (Visual Basic).

  • Obtains an attribute object for the method and attribute type by using MethodInfo.GetCustomAttribute. If GetCustomAttribute returns Nothing (Visual Basic), the method doesn't contain the attribute.

Imports System
Imports System.Collections.Generic
Imports System.Reflection
Imports System.Threading.Tasks
Imports System.Runtime.CompilerServices


Module Module1

    ' This class is used by the code below to discover method attributes. 
    Public Class TheClass
        Public Async Function AsyncMethod() As Task(Of Integer)
            Await Task.Delay(5)
            Return 1
        End Function 

        Public Iterator Function IteratorMethod() As IEnumerable(Of Integer)
            Yield 1
            Yield 2
        End Function 

        Public Function RegularMethod() As Integer 
            Return 0
        End Function 
    End Class 


    Private Function IsAsyncMethod(classType As Type, methodName As String)
        ' Obtain the method with the specified name. 
        Dim method As MethodInfo = classType.GetMethod(methodName)

        Dim attType As Type = GetType(AsyncStateMachineAttribute)

        Dim attrib = CType(method.GetCustomAttribute(attType), AsyncStateMachineAttribute)
        ' The above variable contains the StateMachineType property. 

        Return (attrib IsNot Nothing)
    End Function 

    Private Function IsIteratorMethod(classType As Type, methodName As String)
        ' Obtain the method with the specified name. 
        Dim method As MethodInfo = classType.GetMethod(methodName)

        Dim attType As Type = GetType(IteratorStateMachineAttribute)

        ' Obtain the custom attribute for the method. 
        ' The value returned contains the StateMachineType property. 
        ' Nothing is returned if the attribute isn't present for the method. 
        Dim attrib = CType(method.GetCustomAttribute(attType), IteratorStateMachineAttribute)

        Return (attrib IsNot Nothing)
    End Function 

    Private Sub ShowResult(classType As Type, methodName As String)
        Console.Write((methodName & ": ").PadRight(16))

        If IsAsyncMethod(classType, methodName) Then
            Console.WriteLine("Async method")
        ElseIf IsIteratorMethod(classType, methodName) Then
            Console.WriteLine("Iterator method")
        Else
            Console.WriteLine("Regular method")
        End If 

        ' Note: The IteratorStateMachineAttribute applies to Visual Basic methods 
        ' but not C# methods. 
    End Sub 

    Sub Main()
        ShowResult(GetType(TheClass), "AsyncMethod")
        ShowResult(GetType(TheClass), "IteratorMethod")
        ShowResult(GetType(TheClass), "RegularMethod")

        Console.ReadKey()
    End Sub 

    '   AsyncMethod:    Async method 
    '   IteratorMethod: Iterator method 
    '   RegularMethod:  Regular method 

End Module

.NET Framework

Supported in: 4.5

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, Windows Phone Silverlight 8

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
Was this page helpful?
(1500 characters remaining)
Thank you for your feedback
Show:
© 2014 Microsoft