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:
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.
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.
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
