VB6: Variant Stack Class (Code Library)

This code, when pasted into a Class module provides text box stack functionality.

It supports the following methods and properties:

• Push
• Pull
• IsStackEmpty
• Current

It will dynamically grow the stack as data is added, and will not allow you to pull data once the stack is empty.

The stack will accept variants, which makes it polymorphic, allowing it to accept Objects, integers, dates, strings, collections, or whatevers.

The code:

Private mlngTop As Long
Private mvarStack() As Variant

 

Private Sub Class_Initialize()

 

    ' stack is empty (first element is zero)
    mlngTop = -1

 

    ' stack will start with one element,
    ' it will grow if necessary
    ReDim mvarStack(0) As Variant

 

End Sub

 

Public Property Get IsStackEmpty() As Boolean
    IsStackEmpty = mlngTop < 0
End Property

 

Public Property Get Current() As Variant
    If Not Me.IsStackEmpty Then
        If IsObject(mvarStack(mlngTop)) Then
            Set Current = mvarStack(mlngTop)
        Else
            Current = mvarStack(mlngTop)
        End If
    Else
        Err.Raise 1, "VariantStack", "Stack empty"
    End If
End Property

 

Public Sub Push(ByVal varData As Variant)

 

    ' is array big enough to accomodate stack?
    If mlngTop = UBound(mvarStack) Then
        ReDim Preserve mvarStack(mlngTop + 1) As Variant
    End If
   
    ' add to stack
    mlngTop = mlngTop + 1
   
    ' handle objects and other variable types
    If IsObject(varData) Then
        Set mvarStack(mlngTop) = varData
    Else
        mvarStack(mlngTop) = varData
    End If
   
End Sub

 

Public Function Pull() As Variant
    Pull = Me.Current()
    mvarStack(mlngTop) = Empty ' blank element
    mlngTop = mlngTop - 1
End Function