PredeclaredID

[tiredofit]

Simply looking at this code, it doesn't make sense:

' Standard module

Sub Start()

    Something.Test 1,2

End Sub

'Class called Something

Public Sub Test(Val1, Val2)

End Sub

I didn't expect it to compile because my limited understanding of classes is that one must instantiate before using it.

Then I remembered about some additional settings that classes have, so I exported it, then opened it in notepad.

VERSION 1.0 CLASS
BEGIN
  MultiUse = -1  'True
END
Attribute VB_Name = "Class1"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Option Explicit

Public Sub Test(Val1, Val2)
    
End Sub

I think what made the code compile and run is this line:

Attribute VB_PredeclaredId = True

Can someone please explain what it's doing and if setting it to be true means you don't have to instantiate, then why not set it to be true all the time?

Thanks

 

[RoryA]

Typically you don't need a default instance of a class; the point of them is to be reusable templates.

 

[tiredofit]

Typically you don't need a default instance of a class; the point of them is to be reusable templates.

Thanks

 

[GWteB]

If you change the value of VB_PredeclaredId to true in a class file, that class will be given a named default instance when your code starts running.
In VBA a Userform is a named default instance class by default, class modules aren't. Why? It's by design, ask MS.

As @RoryA pointed out, you want/need to instantiate a class. You always should avoid working directly with the default instance of a class, but one exception could be a factory method built into the class itself. That way the necessary initialization of the object represented by that class can take place immediately with the benefit of using whatever parameters you want.

 

[tiredofit]

If you change the value of VB_PredeclaredId to true in a class file, that class will be given a named default instance when your code starts running.
In VBA a Userform is a named default instance class by default, class modules aren't. Why? It's by design, ask MS.

As @RoryA pointed out, you want/need to instantiate a class. You always should avoid working directly with the default instance of a class, but one exception could be a factory method built into the class itself. That way the necessary initialization of the object represented by that class can take place immediately with the benefit of using whatever parameters you want.

Thanks for the detailed explanation.

I only came across this by accident. Clearly whoever wrote it wanted to demonstrate their detailed understanding of classes.