Binaryworld - CBitArray - a class for dealing with large arrays of Boolean ... [ VB -> Arrays ]

' ------------------------------------------------------------------------
' The CBITARRAY class
'
' simiulates an array of Boolean values
' saves memory by packing one element in one bit
'
' IMPORTANT: you make make ITEM the default member for this class
'      do this from inside the Tools | Procedure Attributes dialog box
'
' Usage:
'  Dim bitArr As New CBitArray
'  bitArr.Init(10000)     ' 10,000 boolean elements
'  ' assign a value
'  bitArr(10) = True
'  ' read it back
'  Print bitArr(10)
'
' ------------------------------------------------------------------------

Option Explicit

Dim mask(0 To 7) As Integer
Dim values() As Byte

Public Sub Init(ByVal numEls As Long)
  ' redimension the internal array
  ' MUST BE THE FIRST METHOD CALLED FOR THIS CLASS
  ReDim values(numEls \ 8) As Byte
End Sub

Private Sub Class_Initialize()
  ' initialize the mask() array
  Dim i As Integer
  mask(0) = 1
  For i = 1 To 7
    mask(i) = mask(i - 1) * 2
  Next
End Sub

' for smoother syntax, you should make ITEM the default member for this class

Property Get Item(ByVal index As Long) As Boolean
  ' retrieve an array item
  Item = values(index \ 8) And mask(index And 7)
End Property

Property Let Item(ByVal index As Long, ByVal new_Item As Boolean)
  Dim ndx As Long, m As Byte
  ' cache the mask into a local variable
  m = mask(index And 7)
  ndx = index \ 8
  ' set or reset only the relevant bit
  values(ndx) = (values(ndx) And Not m) Or (new_Item And m)
End Property