VB6: How to pass temporary to a function in Visual Basic 6

In C++ it is possible to pass a temporary object argument to a function:

struct Foo
{
    Foo(int arg);
    // ...
}

void PrintFoo(const Foo& f);

PrintFoo(Foo(10))

I am trying to implement something similar in Visual Basic 6:

'# Scroll bar params
Public Type ScrollParam开发者_开发知识库s
    sbPos As Long
    sbMin As Long
    sbMax As Long
End Type

Public Function MakeScrollParams(pos As Long, min As Long, max As Long)
    Dim params As ScrollParams
    With params
        .sbPos = pos
        .sbMin = min
        .sbMax = max
    End With
    Set MakeScrollParams = params
End Function

'# Set Scroll bar parameters
Public Sub SetScrollParams(sbType As Long, sbParams As ScrollParams)
    Dim hWnd As Long
    ' ...

End Sub

However, Call SetScrollParams(sbHorizontal, MakeScrollParams(3, 0, 10)) raises an error: ByRef argument type mismatch. Why?

A couple of things need to change from your existing code:

1. You need to strongly-type the declaration of the MakeScrollParams function.

   It returns an instance of the ScrollParams type, so you should specify that explicitly in the declaration. Like so:

   Public Function MakeScrollParams(pos As Long, min As Long, max As Long) As ScrollParams
   

2. You need to remove the Set keyword from the last line in that function in order to avoid an "Object Required" compilation error. You can only use Set with objects, such as instances of classes. For regular value types, you omit it altogether:

   MakeScrollParams = params
   

So the full function declaration would look like this:

Public Function MakeScrollParams(pos As Long, min As Long, max As Long) As ScrollParams
    Dim params As ScrollParams
    With params
        .sbPos = pos
        .sbMin = min
        .sbMax = max
    End With
   MakeScrollParams = params
End Function

And calling it like this:

Call SetScrollParams(sbHorizontal, MakeScrollParams(3, 0, 10))

now works perfectly.

Maybe?

Public Function MakeScrollParams(pos As Long, min As Long, max As Long) As ScrollParams