Traversing and printing complex Dictionary types (Scripting.Dictionary) - Dictionary inside of a Dictionary

Based on this SO post - also reposted on vba4all.com with a few more details and explanations.

Please notice there currently is no error handling whatsoever as I didn't analyse and consider any traps yet. Although feel free to supply details/code based on your assumptions. For Example - the code fails when you try to load duplicate keys into the dictionary... this can easily be handled with the OERN approach...

So the tree would look like this for example

I have created a simple procedure TraverseDictionary() which traverses any structure of dictionaries.

The simplest version that prints somehow a logical structure to the Immediate Window:

Sub Main()

    Dim dict As New Dictionary
    Dim subDict As New Dictionary
    Dim lvlDict As New Dictionary

    lvlDict.Add "LVL KEY", "LVL ITEM"

    subDict.Add "HELLO", ":)"
    subDict.Add "WORLD", ":("
    subDict.Add "OTHER", lvlDict

    dict.Add "FOO", "BAR"
    dict.Add "BOO", subDict

    TraverseDictionary dict

End Sub

Private Sub TraverseDictionary(d As Dictionary)

    For Each Key In d.Keys
        Debug.Print "KEY: " & Key
        If VarType(d(Key)) = 9 Then
            TraverseDictionary d(Key)
        Else
            Debug.Print "ITEM: " & d(Key)
        End If
    Next
End Sub

with a result:

and w/ a print out to sheet with somehow even more logical view

```
Private i As Long
Private depth As Long

Sub Main()
Cells.ClearContents

Dim dict As New Dictionary
Dim subDict As New Dictionary
Dim lvlDict As New Dictionary

lvlDict.Add "LVL KEY", "LVL ITEM"

subDict.Add "HELLO", ":)"
subDict.Add "WORLD", ":("
subDict.Add "OTHER", lvlDict

dict.Add "FOO", "BAR"
dict.Add "BOO", subDict

i = 1
depth = 0
TraverseDictionary dict

Columns.AutoFit

End Sub

Private Sub TraverseDictionary(d As Dictionary)

For Each Key In d.Keys
Range("A" & i).Offset(0, depth) = "KEY: " & Key
If VarType(d(Key)) = 9 Then
depth = depth + 1

A couple of things, which you've really more or less pointed out already.

-
You've shown us two different implementations of the same routine that outputs two two different places. I think what you really need is a class that gets initialized with an IOuput member. Then you can have different implementations of the IOuput interface, but TraverseDictionary only has to deal with IOutput and one routine can print out to anywhere.

-
You're correct that VarType = 9 is unsafe and TypeName = "Dictionary" is safer, but I'm not sure it's entirely safe. What if there's a namespace conflict because I implemented a VBAProject.Dictionary? TypeName of my custom dict would also be "Dictionary" and who knows what would happen then. TypeOf is another option though. I've not tested it, but I believe you can do this.

If TypeOf d(Key) Is Scripting.Dictionary Then

But that means you'll also have to check IsObject(d(key)) prior to checking its actual type as well.

Update:

I finally had time to test this. I created an empty Dictionary class and ran the code below. It works.

Sub test()
    Dim dict As New Scripting.Dictionary
    Dim myDict As New VBAProject.Dictionary

    Debug.Print TypeOf dict Is Scripting.Dictionary
    'true
    Debug.Print TypeOf myDict Is Scripting.Dictionary
    'false
    Debug.Print TypeOf dict Is VBAProject.Dictionary
    'false
    Debug.Print TypeOf myDict Is VBAProject.Dictionary
    'true
End Sub

StackExchange Code Review Q#63353, answer score: 7