VB6 keyword Set what does it mean?

Question

I been browsing an old VB6 code and I saw something like this

 Set AST = CreateObject("ADODB.Stream")

I have experience using VB6 and VB.NET but I never use this keyword Set before in my VB6 projects. I researched a lot in the internet what is the use of Set and what I only know is the usage in Properties which is only I know in VB.NET

Public Property myProperty As String
    Get
      Return _myProperty
    End Get
    Set(value as String)
      _myProperty = value
    End Set
End Property

and I think Set is used differently on the code above. What is the difference of the two approaches? I want to know what does the Set do in VB6

Answer 1

Set is assigning a new reference to the AST variable, rather than assigning a value to (the object currently referenced by AST)'s default property.

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There's not much VB 6 documentation around on the web, but¹ some of the help for VB.Net still references the older ways.

See Default Property Changed for Visual Basic 6 Users:

In Visual Basic 6.0, default properties are supported on objects. On a Label control, for example, Caption is the default property, and the two assignments in the following example are equivalent.

Dim lbl As Label 
lbl = "Important" 
lbl.Caption = "Important" 

While default properties enable a certain amount of shorthand in writing Visual Basic code, they have several drawbacks:

...

• Default properties make the Set statement necessary in the Visual Basic language. The following example shows how Set is needed to indicate that an object reference, rather than a default property, is to be assigned.

Dim lbl1 As Label, lbl2 As Label 
lbl1 = "Saving" ' Assign a value to lbl1's Caption property. 
lbl2 = lbl1       ' Replace lbl2's Caption property with lbl1's. 
Set lbl2 = lbl1   ' Replace lbl2 with an object reference to lbl1. 

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So, in VB.Net, Let and Set became obsolete (in fact, Let was already pretty much obsolete in VB 6) because the language rules changed. An assignment A = B, if A is a reference, is always assigning a new reference to A.

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¹MarkJ has supplied links to the older VB6 documentation in the comments.