Microsoft's Visual Basic (VB) 5.0 development tool offers a new
integrated development environment (IDE), an updated language engine that
provides native code compilation, and a substantial number of features. The new
IDE will make all VB developers more productive, and faster execution of native
code will especially benefit algorithmic-intensive applications and components.
Microsoft gives special emphasis to Internet and intranet
development--particularly the ability to create ActiveX controls--to let VB
developers quickly build and deploy Web-based applications. Developers who use
VB for corporate data access are probably the largest and most visible segment
of VB users. These developers can use the latest versions of VB's data access
engines to take advantage of new features and substantially increased
performance.
Native Code Compilation
The feature developers requested most in VB 5.0 is the ability to compile
source code to natively execuTable code. VB 5.0 uses the same two-pass
compilation process as Visual C++. The first pass parses the code and generates
a preprocessed interim format; the second pass optimizes and generates native
code. VB 5.0 supports several of the same compiler options as VC++. The most
noTable option is the ability to optimize for fast vs. small code.
Although developers were begging for native code, what they really wanted
was the execution speed that comes with natively compiled languages such as C.
Native code offers substantial performance improvements in numeric-intensive
operations, but it isn't a cure-all for every performance bottleneck. Native
code makes sense in a VB application when developers must resort to C for
writing a performance-critical part of the application. With VB 5.0, instead of
learning a new language (or finding someone else to write the code), developers
can now get accepTable performance from a language they already know.
An assumption many people make about native code compilation is that it
eliminates the need for a corresponding runtime. On the contrary, any p-code or
native code component or execuTable still requires the VB 5.0 runtime. This
runtime requirement is not necessarily a bad thing. The alternative to
dynamically loading a common library (which is shared across many applications)
is for each application to statically link to it, thus loading the library into
memory in each process. In practice, of course, the linker works with a standard
library format to pull into the execuTable-only functions that the main program
calls. Unfortunately, Microsoft never designed VB to be a library of discrete
callable routines.
Language Features
VB 5.0 adds several important features to the underlying language engine.
The most useful feature is the ability to create, or source, events. Every
edition of VB has supported event-generating components (e.g., a CommandButton's
Click event). VB 4.0 let developers create object servers that exposed
properties and methods, but signaling between object servers was either
inefficient (using timer-based code to periodically poll an object and check its
status) or complicated (passing an internal object to the server, which
subsequently executed an exposed method to call back into the internal object).
Using VB 5.0, developers can create and handle events.
To the outside world, an object's interfaces (which include its exposed
properties, methods, and events) define the object. Using the component object
model (COM) architecture that underlies Object Linking and Embedding (OLE) and
ActiveX, one advanced component can include the interfaces that another original
component provides. An application that uses the original component could have
the advanced component transparently replace the original component. A powerful
feature of VB 5.0 is its ability to build ActiveX components that expose the
properties and methods (but not, in this release, the events) of one or more
object servers. This feature, which enables multiple implementations of a
particular object specification, lets VB 5.0 developers create polymorphic
objects, according to well-established OOP methodologies.
Fortunately, not all the new features in VB 5.0 relate to creating ActiveX
servers. For instance, developers can use the AddressOf operator to pass the
address of a VB procedure to an external DLL function. This operator lets VB
developers use the Windows API functions that require a fixed callback address.
AddressOf lets you trap any Windows messages sent to a form or control. Previous
versions of VB required developers to use a third-party product to trap these
messages. In addition, when you use AddressOf with the Win32 CreateThread API,
you can create multithreaded applications in VB.
Internet
Most developers knew about VB 5.0's ability to create ActiveX controls long
before Microsoft posted the Control Creation Edition beta on its Web site. You
can use ActiveX controls in non-Web applications (they will be a key technology
in future Microsoft operating systems), but features such as code signing and
progressive downloading of data make ActiveX controls particularly well suited
to Web applications. However, the VB 5.0 runtime requirement poses one problem
for Web applications. To run a VB 5.0 ActiveX control, the VB 5.0 runtime must
be present on the target system. This presence means that the first time you
download a VB 5.0 ActiveX control, you must also undergo the 1.3MB download of
the runtime before you can use the control. The control creation process can be
a little confusing at first, particularly for developers who are not familiar
with writing components.
However, creating ActiveX documents couldn't be easier. VB 5.0 includes a
wizard for converting traditional forms-based VB projects into ActiveX
documents. Unfortunately, VB 5.0-created ActiveX documents don't work the same
as the more familiar server applications such as Word and Excel. Instead of
creating embeddable objects, VB 5.0 uses ActiveX documents to run a VB
application inside a container application such as Internet Explorer (IE) or the
Microsoft Office Binder. Although Microsoft rewrote VB 5.0's Setup Wizard to
handle packaging of ActiveX components for Internet and intranet use, the
process is still complicated and almost always involves a lot of testing.
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