Predict The Output III

[pgc01]

Hi Emma

Great explanation. I am left with one question - why is this even possible in VBA? Under what circumstances would someone want to do this?

This is also a practical example. I posted it 2 weeeks ago to set/reset an attribute of a file:

http://www.mrexcel.com/forum/showthread.php?t=396338

 

[Oorang]

Great explanation. I am left with one question - why is this even possible in VBA? Under what circumstances would someone want to do this?

I suppose the most literal minded way of answering that question would be "because it's possible in VB6 which VBA is based on". As for why would it be possible at all, it's a way to store multiple pieces of information in one simple little number. A long integer is 32 bits. That means you could define 32 Boolean values in one field and store them in a single Long instead of 32 Boolean (true/false) fields. If one were trying to save on storage, or minimize the number of parameters being passed around, this would be pretty handy. A trivial example follows:

Option Explicit

Public Enum eEmployeeData
    'Shifts:
    eFirstShift = 1
    eSecondShift = 2
    eThirdShift = 4
    eSwingShift = 8
    'Pay Type:
    eSalary = 16
    eFullTimeHourly = 32
    ePartTimeHourly = 64
    'Is Contractor?:
    eContractor = 128
    'Status:
    eRetired = 256
    eFired = 512
    eQuit = 1024
    eLaidOff = 2048
    eActive = 4096
    [_max] = 4096
End Enum

Public Type EmployeeInfo
    Name As String
    Data As eEmployeeData
End Type

Sub Example()
    Dim employee As EmployeeInfo
    employee.Name = "John Q. Public"
    employee.Data = eActive + eContractor + eFirstShift + eFullTimeHourly
    MsgBox "So from this one little number """ & employee.Data & """, we know all of this about " & employee.Name & ":" & DataToString(employee.Data)
End Sub

Private Function DataToString(ByVal dataValue As eEmployeeData) As String
    Dim strRtnVal As String
    Dim lngExp As Long
    For lngExp = 0 To Log2(eEmployeeData.[_max])
        Select Case dataValue And (2 ^ lngExp)
        Case eFirstShift:       strRtnVal = strRtnVal & vbCr & "eFirstShift"
        Case eSecondShift:      strRtnVal = strRtnVal & vbCr & "eSecondShift"
        Case eThirdShift:       strRtnVal = strRtnVal & vbCr & "eThirdShift"
        Case eSwingShift:       strRtnVal = strRtnVal & vbCr & "eSwingShift"
        Case eSalary:           strRtnVal = strRtnVal & vbCr & "eSalary"
        Case eFullTimeHourly:   strRtnVal = strRtnVal & vbCr & "eFullTimeHourly"
        Case ePartTimeHourly:   strRtnVal = strRtnVal & vbCr & "ePartTimeHourly"
        Case eContractor:       strRtnVal = strRtnVal & vbCr & "eContractor"
        Case eRetired:          strRtnVal = strRtnVal & vbCr & "eRetired"
        Case eFired:            strRtnVal = strRtnVal & vbCr & "eFired"
        Case eQuit:             strRtnVal = strRtnVal & vbCr & "eQuit"
        Case eLaidOff:          strRtnVal = strRtnVal & vbCr & "eLaidOff"
        Case eActive:           strRtnVal = strRtnVal & vbCr & "eActive"
        End Select
    Next
    DataToString = strRtnVal
End Function

Private Function Log2(ByVal value As Long) As Long
    Const dblLog2_c As Double = 0.693147180559945
    Log2 = Log(value) / dblLog2_c
End Function