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When I set a variable to an object in VBA / VBScript, I always need to prefix the statement with "Set" such as: Set Dict = CreateObject("Scripting.Dictionary")

If I set a variable to a primitive or array value, I have to omit the "Set" such as: Num = 123

This is different from languages such as JavaScript, PHP, Python etc. Is there some technical reason why they have this requirement in VBA / VBScript?

Brian
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neelsg
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    http://stackoverflow.com/questions/349613/what-does-the-keyword-set-actually-do-in-vba – devnull May 21 '14 at 07:51
  • COM objects are not native to VB, its a case of a non OO language interfacing with an OO API, rather than re-write the whole of basic from scratch they tacked on the "Set" keyword to allow VB to attach to COM objects. – James Anderson May 21 '14 at 08:22

2 Answers2

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VB and VBA had something called "default properties". If your code mentioned the object without any property/ method specified, then you got the default property, not the object!

Dim vValue as Variant

vValue = textBox1

? TypeName( vValue )

String

Should this work? Well, yes, because VB interprets this as ...

vValue = textBox1.Text

... because Text is the textbox's default property.

The Set statement overrides all that, forcing VB to use the object itself.

Set vValue = textBox1

? TypeName( vValue )

TextBox

Community
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Phill W.
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    While this is an interesting side effect of the `Set` semantics, it's not really an answer to the question. – Avner Shahar-Kashtan May 21 '14 at 11:47
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    @AvnerShahar-Kashtan - I'd say it's an interesting side effect of not using Set. – JeffO May 21 '14 at 11:59
  • Should "sValue" above be "vValue"? If so, then I think this answers the original question very well. If not, then I don't understand this answer at all as nothing is ever assigned to vValue. – OldFart May 21 '14 at 21:18
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    @AvnerShahar-Kashtan: It's not a side-effect - it's a requirement of the language. If you want to work with an object reference then you MUST use the Set statement. If you're happy to work with every object's default property, then you can leave it out. Omitting default properties from Visual Basic.Net was, IMHO, one of the better things Our Friends in Redmond did with the language (sadly, I believe they've reappeared in more recent versions). – Phill W. May 22 '14 at 14:26
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    This *does* answer the original question. The only reason for `Set` is to avoid ambiguity. Without Set, you wouldn't know whether you're assigning an object reference or the object's default property. In VB .NET this is avoided because there are no default properties (except for indexed properties and/or iterators, but those avoid the ambiguity due to their different syntax). – Kyralessa May 22 '14 at 16:13
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Note: when I say "Visual Basic" here I mean Visual Basic 6 and before - not Visual Basic.NET.

Visual Basic is designed to be easy to use. Pointers are hard - and to some extent, so are reference types, like the ones used for objects in most modern languages.

the Set syntax is a way to hide this:

Set foo = Bar() 'Treat foo as reference variable
foo = Bar() 'Treat foo as a value variable

So, people that don't understand references can use objects like value variables, which are easier to grasp. Given that Visual Basic is usually used with the Visual Studio form designer to create GUI applications, you can do quite a lot without using references.

VBA and VBS usually require more reference usage(in VBA you usually need to use Office objects, and in VBS you usually need to use COM objects to interact with Windows), but their syntax still needs to follow the Visual Basic one so they also require the Set syntax.

Idan Arye
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