Using another interface

The Global Wizard program picks which conversion it wants to perform through some logic that we don’t care about, and sends the results to the following function:

Sub UpdateTargetFileDisplay()
    HourGlass Me
    
    ‘ Select the appropriate filter and assign to any old object
    Dim filterobj As Object
    Select Case emtCur
    Case emtStandard
        If chkDelegate Then
            ‘ Translates standard module to global class with delegation
            Set filterobj = New CModGlobDelFilter
        Else
            ‘ Translates standard module to global class w/o delegation
            Set filterobj = New CModGlobFilter
        End If
    Case emtClassPublic
        ‘ Translates public class to private class
        Set filterobj = New CPubPrivFilter
    Case emtClassGlobal
        ‘ Translates global class to standard module
        Set filterobj = New CGlobModFilter
    Case emtClassPrivate
        ‘ Translates private class to public class
        Set filterobj = New CPrivPubFilter
    Case Else
        txtDst = ““
        Exit Sub
    End Select
    ‘ Setting name isn’t performance sensitive, so do it late bound
    filterobj.Name = txtDstModName
    
    ‘ Use early-bound variable for performance sensitive filter
    Dim filter As IFilter
    Set filter = filterobj
    filter.Source = txtSrc
    FilterText filter
    txtDst = filter.Target
    HourGlass Me
End Sub

You might recall my saying at the start of this chapter that the Object type and late binding are evil, and yet look at the type of the filterobj variable at the top of this procedure. Call me a liar. Call me a realist. All these filter classes have a Name property, but it’s set only once. No one will be able to tell the difference if the class-specific objects are bound late rather than early. On the other hand, the properties and methods of the IFilter variable passed to FilterText will be called over and over. You’d notice the difference on large conversion operations if you passed a variable with Object type rather than IFilter type.