Basic disagreements

Developers who think of Visual Basic as a container for their own intellectual property have objected to the idea that the semantics of their chosen language are subject to significant change in the interest of tracking Microsoft's platform evolution. It's clear, though, in Visual Studio 2005 that Microsoft hasn't changed its mind about that doctrine—and that the company recognizes the continuing need to assuage the offended Visual Basic 6 community.

Visual Studio 2005's online documentation includes extensive discussion of the transition from Visual Basic 6 to Visual Basic 2005—more than a little odd, considering that Visual Basic 6 was, in theory, left behind three years ago, but Microsoft isn't letting pride get in the way of pragmatically admitting that many Visual Basic 6 developers didn't make the .Net move.

How big are the differences between Visual Basic 6 and Visual Basic 2005? For coders, there's nothing more fundamental than bitwise (Boolean) logic, and Visual Studio 2005 changes the vocabulary of operators that are available for bit-by-bit comparison of data values. The Visual Basic 6 logical implication operator Imp disappears in Visual Basic 2005, with instructions to replace any use of Imp with a logically equivalent expression combining the operators Not and Or. At least this change can be made by a simple substitution based on patterns of text, unlike some of the language changes.

Much less automatic is the question of whether a developer should replace any given use of the Visual Basic 6 And or Or operators, which evaluate all their arguments, with the Visual Basic 2005 alternatives AndAlso or OrElse: The latter variants stop evaluating arguments as soon as the value of a composite expression can be determined, speeding execution but altering behavior when expression evaluations have side effects.

For example, as soon as an AndAlso encounters an argument that's false, it knows that the truth or falsity of other arguments isn't going to change the falsity of the returned result. It can therefore "short-circuit" that evaluation (as this practice is commonly known), but this means that a subsequent argument to the AndElse operator won't always be evaluated. If that argument is an expression that has a side effect, such as altering the value of a variable, then this represents a change in program behavior.

Other issues for the Visual Basic 6 developer range from changes in the values of system-level constants to the disappearance of traditional control-flow statements such as On...GoSub—changes that have led some protesting developers to dub the current language Visual Fred, arguing that it's a fine and modern language, but it isn't Basic.

Developers in any language should consider the similar question: "Is Visual Studio 2005 the tool that I want?" Microsoft offers developers a comprehensive, impressively choreographed environment for building a broad variety of applications that include both rich clients and Web services. It's up to developers to look in the shadows as well as admire what's deservedly in the spotlight of this high-profile debut.

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