[VB] Patterns / Additional Case Clauses

[AdamSpeight2008]

Is VB going to support patterns?
What about guard clauses? eg Case ... .... When boolEpxr
What about type matching and value manifesting? eg TypeIs String As str
How will tuple clause be handled?

Select Case obj
  Case TypeIs String As str When str IsNot Nothing
    ' do stuff
  Case ( TypeIs Boolean As valid, TypeIs Int32 As i32 ) When ( valid AndAlso ( i32 > 0 ) )
   ' manifesting into Tuple(Of Boolean, Int32 ), which has named elements ( valid:= , i32:= ) 
End Select

[markhurd]

BTW In VB would that When str IsNot Nothing clause be redundant like I believe it would be in C#'s scenario? Clearly, VB has different issues regarding Nothing when considering strings, but has this been confirmed (because it definitely makes some sense for other reference types to not match Nothing)?

[AdamSpeight2008]

@markhurd not necessarily. It makes more sense to leave the when clause as a general boolean expression.

Select Case obj
  Case TypeIs String As str
   ' Manifests variable, or set value of. eg  str = DirectCast( obj, Sting )
   ' Note: str could be null ( eg default(String) )
    Select Case True

      Case Else When str IsNot Nothing
    ' Handle non null string case

      Case Else When str Is Nothing
    'Handle null string case

    End Select

End Select

'TypeIs obj As T` would be also applicable in if statements.

If TypeIs obj As str Then
  ' str = DirectCast( obj , String )
Else

End If

[AdamSpeight2008]

(Ported to VBLang)