No More Underscores in VB 10

Posted by Al Tenhundfeld on Apr 08, 2009

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Development,

Architecture & Design

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.NET Framework ,

.NET ,

Language Design

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Visual Basic.NET

Visual Basic 10 will have an improved compiler that makes underscores optional for most line continuations. This represents a significant change for VB, traditionally a line-terminated language. The Visual Basic team has an in-depth explanation of Implicit Line Continuation.

VB 1-6 and VB.NET (7-9) used the carriage return as a statement termination token, similar to the explicit semicolon ";" in C#. By moving to an implicit termination token, Visual Basic language readability will be greatly improved, especially when writing multi-line LINQ queries.

Dim dates = from d in listOfDates _
		where d.Year > 2009 _
		select d _
		distinct _ 
		order by d

Could become:

Dim dates = from d in listOfDates 
		where d.Year > 2009 
		select d 
		distinct  
		order by d

The VB team explanation mentioned above covers specific cases where implicit line continuation is not supported:

We don’t capture every scenario. Given our cost and time constraints around the feature, we tried to capture the most common cases that would provide the most bang for the buck. We also avoided the ones that just led to problems. Here are some examples of problems you could have if we had decided to allow implicit continuation anywhere. I take these from some analysis that Lucian Wischik (also on the VB compiler team) did on our grammar:

With y
	A=x
       .xfield
End With

If we allowed implicit continuation before the ‘.’ we would have problems knowing what the period belongs to. For example, it could be interpreted as:

With y
	A=x.xield
End With

Or

With y
        A=x
       .xfield
End With

Channel 9 also has an excellent interview with Tyler Whitney, a developer on the Visual Basic compiler team.

1. Back to top

   Huh?

   by Steve Macdonald

   This makes me really glad I finally bit the bullet last year and switched from VB (since VB 1.0) to C#.
   
   What could be more confusing than a line termination scheme that only applies some of the time?
   
   Phase out VB. Keep C# lean. Bring Ruby and Python fully into .Net

   Reply

2. Back to top

   Re: Huh?

   by Al Tenhundfeld

   That was my first impression also. If you watch the Channel 9 video, it seems less heinous, though still a little mysterious.
   
   But if they want to go this route, why not just make VB have an explicit terminator, like ";". Yeah, it breaks backwards compatibility, but the upgrade process would be a fairly trivial text replace.
   
   And it's time for VB to lose some of its cruft. If you're programming in VB.NET without Option Strict, you're doing it wrong, IMO.

   Reply

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   Re: Huh?

   by Jack Singleton

   Although, Ruby and Python both have a "line termination scheme that applies some of the time"... ;)

   Reply

4. Back to top

   Re: Huh?

   by Steve Macdonald

   Heh. Good point. I'm not a Ruby or Python programmer, but that's good to know!

   Reply

5. Back to top

   I Like It

   by Casey Joyce

   I like the new syntax and I think the VB team has done a good job to eliminate the scenarios that would be ambiguous. The improved readability and aesthetics are worth it.

   Reply

6. Back to top

   Re: Huh?

   by Jonathan Allen

   Although, Ruby and Python both have a "line termination scheme that applies some of the time"... ;)

   
   
   As does many variants of SQL.

   Reply

7. Back to top

   Re: Huh?

   by Jonathan Allen

   And it's time for VB to lose some of its cruft. If you're programming in VB.NET without Option Strict, you're doing it wrong, IMO.

   
   
   Wait a second. If you are working with COM, using Option Strict is downright painful. (Though not as bad as C#.)

   Reply

8. Back to top

   Re: Huh?

   by Jonathan Allen

   What could be more confusing than a line termination scheme that only applies some of the time?

   
   
   I know!
   
   Having lines broken at random like they are in C#. Then spending weeks arguing over coding conventions, only to repeat the argument every time a new team member is hired.

   Reply

9. Back to top

   Re: Huh?

   by Al Tenhundfeld

   OK, you're right. I try to avoid working directly with COM; so it's not on my mind.

   Reply

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