VB6 - Resource with object passing to procedures

[Lextar]

When you declare a procedure and pass an object to it, e.g.

Public Sub MakeVisible(item as Object)
item.visible = true
end sub

How does VB handle the resource? when you call the procedure

Call MakeVisible(Button1)
Call MakeCisible(Form1)

Does it make a copy of the object and pass to the procedure, or does the ByRef default actually just pass a refernce?

Its the passing a whole copy of the object that I am worried about if it does do that.

[David Smith]

In VB6, when you pass an object to a procedure, such as in your example Public Sub MakeVisible(item As Object), VB6 passes a reference to the object by default (ByRef). This means the procedure operates on the original object without creating a full copy, ensuring efficient memory use.

Explanation:

1. ByRef Default Behavior:

   • In VB6, parameters are passed ByRef by default unless explicitly declared with ByVal.
   • Passing Button1 or Form1 to MakeVisible(item As Object) means the procedure receives a reference to these objects. Changes to their properties or methods in the procedure directly affect the original objects.

2. No Full Object Copy:

   • VB6 does not create a deep copy of the object when passed as a parameter. Even if you use ByVal, only the reference itself is copied, not the underlying object. This ensures changes to the object's properties, like setting item.Visible = True, modify the actual instance.

3. Efficiency and Risks:

   • This behavior optimizes resource use but requires careful handling. For instance, unintended changes to an object's state persist outside the procedure, which may lead to side effects.

Related Insight:

This concept is particularly relevant in VB6 to .NET conversion, where VB6's ByRef mechanism contrasts with .NET's enhanced type-safety and explicit reference-passing features. In .NET, you can use ref or out parameters in C#, or manage object references explicitly in VB.NET to align with VB6's behavior. Understanding how VB6 handles objects is crucial to ensuring a seamless migration process, avoiding pitfalls like unexpected behavior due to default reference-passing mechanisms​

[Malini Selvarasu]

Hi ,

We believe that the previous update should have resolved your issue. If you encounter any new issues, please feel free to create a new forum, and we will be happy to assist you.

Regards,
Malini Selvarasu