VB.Net/Data Structure/IEnumerable

IEnumerable: array like access

Imports System
Imports System.Collections
 
Public Class MainClass
    Shared Sub Main(ByVal args As String())
             " create a new list box and initialize
             Dim currentListBox As New EnumerableClass("A", "B")
             " add a few strings
             currentListBox.Add("C")
             currentListBox.Add("D")
             currentListBox.Add("E")
             currentListBox.Add("F")
             " test the access
             Dim subst As String = "Z"
             currentListBox(1) = subst
             " access all the strings
             Dim s As String
             For Each s In currentListBox
                 Console.WriteLine("Value: {0}", s)
             Next
    End Sub
End Class
     Public Class EnumerableClass : Implements IEnumerable
         Private strings( ) As String
         Private ctr As Integer = 0
         Private Class MyEnumerator
             Implements IEnumerator
             Private currentListBox As EnumerableClass
             Private index As Integer
             Public Sub New(ByVal currentListBox As EnumerableClass)
                 Me.currentListBox = currentListBox
                 index = -1
             End Sub
             Public Function MoveNext( ) As Boolean _
               Implements IEnumerator.MoveNext
                 index += 1
                 If index >= currentListBox.strings.Length Then
                     Return False
                 Else
                     Return True
                 End If
             End Function
             Public Sub Reset( ) _
               Implements IEnumerator.Reset
                 index = -1
             End Sub
             Public ReadOnly Property Current( ) As Object _
             Implements IEnumerator.Current
                 Get
                     Return currentListBox(index)
                 End Get
             End Property
         End Class  " end nested class
         Public Function GetEnumerator( ) As IEnumerator _
         Implements IEnumerable.GetEnumerator
             Return New MyEnumerator(Me)
         End Function
         Public Sub New( _
           ByVal ParamArray initialStrings( ) As String)
             ReDim strings(7)
             Dim s As String
             For Each s In initialStrings
                 strings(ctr) = s
                 ctr += 1
             Next
         End Sub
         Public Sub Add(ByVal theString As String)
             strings(ctr) = theString
             ctr += 1
         End Sub
         Default Public Property Item( _
           ByVal index As Integer) As String
             Get
                 If index < 0 Or index >= strings.Length Then
                     " handle bad index
                     Exit Property
                 End If
                 Return strings(index)
             End Get
             Set(ByVal Value As String)
                 strings(index) = Value
             End Set
         End Property
         Public Function GetNumEntries( ) As Integer
             Return ctr
         End Function
     End Class

Implements IEnumerable

Imports System
Imports System.Collections
Public Class MainClass
    
    Shared Sub Main()
       Dim currentListBox As New _
           ListBoxTest("Hello", "World")
       "add a few strings
       currentListBox.Add("o")
       currentListBox.Add("s")
       currentListBox.Add("n")
       currentListBox.Add("t")
       "test the access
       Dim subst As String = "Universe"
       currentListBox(1) = subst
       "access all the strings
       Dim s As String
       For Each s In currentListBox
           Console.WriteLine("Value: {0}", s)
       Next
   End Sub
End Class
     Public Class ListBoxTest : Implements IEnumerable
         Private strings(  ) As String
         Private ctr As Integer = 0
         Private Class ListBoxEnumerator
             Implements IEnumerator
             Private currentListBox As ListBoxTest
             Private index As Integer
             Public Sub New(ByVal currentListBox As ListBoxTest)
                 Me.currentListBox = currentListBox
                 index = -1
             End Sub
             Public Function MoveNext(  ) As Boolean _
               Implements IEnumerator.MoveNext
                 index += 1
                 If index >= currentListBox.strings.Length Then
                     Return False
                 Else
                     Return True
                 End If
             End Function
             Public Sub Reset(  ) _
               Implements IEnumerator.Reset
                 index = -1
             End Sub
             Public ReadOnly Property Current(  ) As Object _
             Implements IEnumerator.Current
                 Get
                     Return currentListBox(index)
                 End Get
             End Property
         End Class 
         Public Function GetEnumerator(  ) As IEnumerator _
         Implements IEnumerable.GetEnumerator
             Return New ListBoxEnumerator(Me)
         End Function
         Public Sub New( _
           ByVal ParamArray initialStrings(  ) As String)
             ReDim strings(7)
             Dim s As String
             For Each s In initialStrings
                 strings(ctr) = s
                 ctr += 1
             Next
         End Sub
         Public Sub Add(ByVal theString As String)
             strings(ctr) = theString
             ctr += 1
         End Sub
         Default Public Property Item( _
           ByVal index As Integer) As String
             Get
                 If index < 0 Or index >= strings.Length Then
                     " handle bad index
                     Exit Property
                 End If
                 Return strings(index)
             End Get
             Set(ByVal Value As String)
                 strings(index) = Value
             End Set
         End Property
         Public Function GetNumEntries(  ) As Integer
             Return ctr
         End Function
     End Class