A Simple Stack Class

This class module functions as a simple stack that can be dropped straight into any project requiring a stack object.

The class contains an internal collection of objects (variants) – you can simply change the data types passed in through the Push method and returned from the Pop method to use any data type you like.

The Push / Pop functionality comes from using the internal Collections Add method with the underused ‘Before’ parameter set as 1.

Simply paste the code into a class module with a relevant name, eg. cStack and you can use it straight away in your projects :

option Explicit
'
' cStack.cls
'
' This class implements a simple stack structure -
' at the moment it only uses a variant item in the
' collection, but of course you can use any
' variable / object type you like!


'
' Our Internal Collection
'
private mStackCollection as Collection

private Sub Class_Initialize()
'
' Create the internal collection
'
    set mStackCollection = new Collection
End Sub

private Sub Class_Terminate()
'
' Kill off the internal collection
'
    set mStackCollection = nothing
End Sub

public Sub Push(byval vData as Variant)
'
' Push an item onto the stack
'

'
' If there's stuff already on the stack, then
' insert the new item before the first item
'
    If mStackCollection.Count > 0 then
        mStackCollection.Add vData, , 1
    else
'
' Otherwise, just add it to the stack as the first item
'
        mStackCollection.Add vData
    End If
End Sub

public Function Pop() as Variant
'
' 'Pop' an item off the stack
'
    If mStackCollection.Count > 0 then
        If IsObject(mStackCollection.Item(1)) then
            set Pop = mStackCollection.Item(1)
        else
            Pop = mStackCollection.Item(1)
        End If
'
' Don't forget to remove the item from the stack
' once it's been popped !
'
        mStackCollection.Remove 1
    else
        Err.Raise vbObjectError + 4999, "cStack::Pop", _
                  "Stack is empty"
    End If

End Function

public property get StackCount() as Long
'
' Number of items in stack
'
    StackCount = mStackCollection.Count
End property
'
'

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