Question

This should be a fairly common question, but I haven’t found a straightforward answer anywhere.

If I instantiate an object within a function in VB.NET and return it, does it return it by reference or by value. IE – should I be worried about performance if I write something like this:

Public Function ret_obj_func() As big_object
    Dim ret_obj As New big_obj(<lots of stuff>)
    Return ret_obj
End Function

If I call this function from somewhere else, will it instantiate the object in the ret_obj and then create a deep copy to pass back a copy to the caller, Or will it just pass back a reference?

Answer 1

It just passes back a reference (assuming big_obj is a class). I wouldn’t use the term “by reference” here, as that has a subtly different meaning when it comes to parameter passing – but assuming big_obj is a class – a reference type – the value of ret_obj is a reference, and that reference will be what’s returned.

I don’t have any articles on this from a VB perspective, but if you’re happy to look at C#, you may find these articles useful:

• Reference and value types
• Parameter passing in C#