Is scoping broken in VBA?

Question

Say you have this code in a module called Module1:

Option Explicit

Private Type TSomething
    Foo As Integer
    Bar As Integer
End Type

Public Something As TSomething

In equivalent C# code if you made the Something field public, the code would no longer compile, because of inconsistent accessibility - the type of the field being less accessible than the field itself. Which makes sense.

However in VBA you could have this code in Module2:

Sub DoSomething()
    Module1.Something.Bar = 42
    Debug.Print Module1.Something.Bar
End Sub

And you get IntelliSense while typing it, and it compiles, and it runs, and it outputs 42.

Why? How does it even work, from a COM standpoint? Is it part of the language specs?

Answer 1

As per my comment, VBA exposes a private Type, just like it exposes a Private Enum.

VBA assumes you can make use of the TypeInfo in the consuming context, but it won't allow you to declare or create instances of those types or enums.

This C++ answer is partly informative:

Access Control is applied to names

The access specifier for the name has nothing to do with it's type

But it's perhaps useful to think of a Private Type in a standard module, as something like a "PublicNotCreatable" class. If you provide a public wrapper, then the type is accessible outside the host module.

But VBA handles things differently when the Type is in a Public Class Module!

Here's your Module1 expanded:

Option Explicit

Private Type TSomething
    Foo As Integer
    Bar As Integer
End Type

Public Type TOtherThing
    Foo As Integer
    Bar As Integer
End Type

Public Type TWrapperThing
  Something As TSomething
End Type

Public Something As TSomething
Public Otherthing As TOtherThing
Public Wrapperthing As TWrapperThing

Public Function GetSomething() As TSomething
  GetSomething.Foo = 1
End Function

Public Function GetOtherthing() As TOtherThing
  GetOtherthing.Foo = 1
End Function

And Module2 expanded:

Option Explicit

Sub DoThings()

'Compile Error: User-defined type not defined
  'Dim oSomething As TSomething
  Dim vSomething As Variant
  
  Dim oOtherthing As Module1.TOtherThing
  Dim vOtherthing As Variant
  Dim oWrapperthing As Module1.TWrapperThing
  
  Module1.Something.Foo = 42
  Module1.Otherthing.Foo = 42
  Module1.Wrapperthing.Something.Foo = 42

  'Compile Error: Only user-defined types defined in public object modules can be coerced to or from a variant or passed to late-bound functions
  'vSomething = Module1.Something
  'vOtherthing = Module1.Otherthing
  
  oOtherthing = Module1.Otherthing
  oOtherthing.Foo = 43
  
  'Is 43 > 42?
  Debug.Assert oOtherthing.Foo > Module1.Otherthing.Foo
  
'Compile Errors: "GetSomething" User-defined type not defined
  'Module1.GetSomething.Foo = 42
  'Module1.GetSomething().Foo = 42
  
  Module1.GetOtherthing.Foo = 42
  Module1.GetOtherthing().Foo = 42

End Sub