VBA's Collection class is lacking so I created a basic List class using Python's as a template. This could make future derived classes easier to implement.
The biggest features are better setting and accessing of values. But one neat-o feature is Python-style indexing.
Dim myList As List
myList.Extend(Array(1,2,3,4,5,6))
Debug.Print myList(-2) ' 5
Debug.print myList.Slice(-1, 1).ToString '"[6,5,4,3,2,1]"
Note: I kept VBA's 1 offset for collections. This means that there is a hole at index 0 and will always return subscript out of range. I don't like it but this way List's will play nice with VBA's collection objects.
Private members
Option Explicit
Private collec As Collection ' Sole datamember
TransformIndex: Enforces Zero Offset and Cylcing.
Private Sub TransformIndex(ByRef x As Variant)
If x < 0 Then x = x + collec.Count + 1
End Sub
Replace is private; use Item and Slice to actually replace elements
Private Sub Replace(ByVal index As Long, ByVal element As Variant)
collec.Remove index
If index = collec.Count + 1 Then
collec.Add element
Else
collec.Add element, before:=index
End If
End Sub
Some boring stuff
Private Sub Class_Initialize()
Set collec = New Collection
End Sub
Private Sub Class_Terminate()
Set collec = Nothing
End Sub
Public Property Get NewEnum() As IUnknown
Attribute NewEnum.VB_UserMemId = -4
Set NewEnum = collec.[_NewEnum]
End Property
Public Methods
The general pattern for these is and implementation of one action for a single element and another for a sequence of elements. e.g. Item and then Slice or Append and Extend. The only exception is removal that only implements single elements.
Accessers and Replacement
Item and Slice provide general access to members and allows replacement as they are not read only.
Public Property Let Item(ByVal index As Long, ByVal element As Variant)
Attribute Item.VB_UserMemId = 0
TransformIndex index
Replace index, element
End Property
Public Property Set Item(ByVal index As Long, ByVal element As Variant)
Attribute Item.VB_UserMemId = 0
TransformIndex index
Replace index, element
End Property
seq is an auxiliary module for general sequence functions. For purposes of this review assume functions from it does exactly what it should do. seq.Assign(x,y) assign's or sets x to y.
Public Property Get Item(ByVal index As Long) As Variant
Attribute Item.VB_UserMemId = 0
TransformIndex index
seq.Assign Item, collec.Item(index)
End Property
Slice: Allows for accessing sub sequences from a to b. Regardless of the order. You can specify a step s to skip elements but note that s must be a natural number. If you want to get a reversed sequence make b less than a not a negative s.
Also Slice is read-write, so it allows replacement of sub-sequences.
Public Property Get Slice(ByVal a As Long, ByVal b As Long, Optional ByVal s As Long = 1) As List
TransformIndex a
TransformIndex b
Set Slice = New List
If s < 1 Then Err.Raise "List.Slice", "Step " & s & " is not a natural number."
s = IIF(a < b, s, -s)
Dim i As Long
For i = a To b Step s
Slice.Append collec.Item(i)
Next i
End Property
Public Property Let Slice(ByVal a As Long, ByVal b As Long, Optional ByVal s As Long = 1, ByVal sequence As Variant)
TransformIndex a
TransformIndex b
If s < 1 Then Err.Raise "List.Slice", "Step " & s & " is not a natural number."
s = IIF(a < b, s, -s)
If Abs(a - b) + 1 <> seq.Length(sequence) Then
Err.Raise 9, "List.Slice", "Subscript out of Range."
End If
Dim i As Long: i = a
Dim element As Variant
For Each element In sequence
Replace i, element
i = i + s
Next element
Debug.Assert (i - s = b)
End Property
Removal Methods
Public Sub Remove(ByVal index As Long)
TransformIndex index
collec.Remove index
End Sub
''
' List.Clear(x, y) \equiv List.Clear(y, x)
Public Sub Clear(ByVal a As Long, ByVal b As Long)
TransformIndex a
TransformIndex b
' Order of removal is irrelevant
If a > b Then seq.Swap a, b
Dim i As Long
For i = 0 To b - a
collec.Remove a
Next i
End Sub
I have been trying to work out a Added a RemoveRange function. I will update with them later.Clear function. Note List.Clear(x, y) \$ \equiv \$ List.Clear(y, x).
Appending Methods
Public Sub Append(ByVal element As Variant)
collec.Add element
End Sub
Public Sub Extend(ByVal sequence As Variant)
Dim element As Variant
For Each element In sequence
collec.Add element
Next element
End Sub
Insertion Methods
Public Sub Emplace(ByVal index As Long, ByVal element As Variant)
TransformIndex index
collec.Add element, before:=index
End Sub
Public Sub Insert(ByVal index As Long, ByVal sequence As Variant)
TransformIndex index
seq.Reverse sequence
Dim element As Variant
For Each element In sequence
collec.Add element, before:=index
Next element
End Sub
Auxiliary Methods
Public Property Get Count() As Long
Count = collec.Count
End Property
Public Function Exists(ByVal sought As Variant) As Boolean
Exists = True
Dim element As Variant
For Each element In collec
If element = sought Then Exit Function
Next element
Exists = False
End Function
Public Property Get ToString() As String
ToString = "[" & Join(seq.ToArray(collec), ", ") & "]"
End Property
