A Look under the hood of the .NET Framework

Namespace ForEachExamples
	Public NotInheritable Class ForEachExamples

		Private Sub New()
		End Sub

		Public Shared Sub ForEach(ByVal l As IEnumerable, ByVal handler As Action(Of Object))
			For Each obj As Object In l
				handler.Invoke(obj)
			Next
		End Sub

		Public Shared Sub ForEachRewritten(ByVal l As IEnumerable, ByVal handler As Action(Of Object))
			Dim e As IEnumerator
			Try
				Dim obj As Object
				e = l.GetEnumerator
				Do While e.MoveNext
					obj = e.Current
					handler.Invoke(obj)
				Loop
			Finally
				If TryCast(e, IDisposable) IsNot Nothing Then
					DirectCast(e, IDisposable).Dispose()
				End If
			End Try
		End Sub

		Public Shared Sub GenericForEach(Of T)(ByVal l As IEnumerable(Of T), ByVal handler As Action(Of T))
			For Each obj As T In l
				handler.Invoke(obj)
			Next
		End Sub

		Public Shared Sub GenericForEachRewritten(Of T)(ByVal l As IEnumerable(Of T), ByVal handler As Action(Of T))
			Dim e As IEnumerator(Of T)
			Try
				Dim obj As T
				e = l.GetEnumerator
				Do While e.MoveNext
					obj = e.Current
					handler.Invoke(obj)
				Loop
			Finally
				If e IsNot Nothing Then
					e.Dispose()
				End If
			End Try
		End Sub

	End Class
End Namespace