System Improvements Create Opportunity
The Ada programming language was revamped in the same year as
MicroSoft Windows, which was a serendipitous bit of luck for R.R. Software. The Madison, Wis.,
company took advantage of the two systems' improvements to create a binding
between them called "Claw."
Currently in beta release, the binding and GUI builder in one
is a tool for creating applications using Microsoft's Windows
interfaces.
Developing Claw
The Ada 95 GUI Binding and Tools for Microsoft Windows 95 is
one of the projects funded by the Ada Joint Program Office's
Ada Technology Insertion Program-Partnerships (ATIP-P).
Their motivation for funding the development of a Windows 95 binding
was strong: X-Windows bindings put software engineers through the
horrors of non-standardization, from which Ada 83 was supposed to
protect them. There were 10 different specifications for Xlib, Xt,
and Motif -- most were incomplete and all incompatible with each other. The
decade of recoding and testing GUIs opened the Ada community's eyes
to the importance of committing money up-front to the creation of a
single robust binding.
R.R. Software specifically designed its GUI binding and tools to be
compatible with four groups of compilers -- its own, Thompson Software's,
Rational's, and the freeware GNAT. Because Ada compilers must all
pass the same suite of tests in order for the government to "validate"
them, R.R. Software's Randall L. Brukardt is confident that, if the binding and GUI builder
run on these four compilers, they will run universally. The
company plans to have a set-up program that will slightly tailor the binding
for different compilers and, otherwise, be completely portable.
In the best case scenario for R.R. Software, compiler vendors will
package their products with the Claw binding rather than commit funds to
create their own. As Brukardt says, "It's good for Ada too, since if
people develop their own bindings, we have another example of the
Tower of Babel."
Another factor motivating the bid for a standard binding was the immense
difficulty of programming in Ada for a Windows application before 1995.
C and C++ programmers could access Win32 directly. An Ada 83 programmer
developing a Windows application would have to write C code in Ada syntax,
which, Brukardt points out, is "unnatural coding." Some bindings do exist
now for the Microsoft Windows 95 operating system, but are they insufficient.
R.R.'s current compilers, for example, only cover about a third of Win32.
Claw's Capabilities
R.R. Software demonstrated Claw, which runs equally on Microsoft's
Windows 95 and Windows NT operating systems, at the TRI-Ada trade
show in December 1996.
Its capabilities were described in the following example, where a
developer is creating an Ada 95 application with a Windows 95 interface
to monitor the air pollution of a factory. The developer wants to
design a large window that displays the day's data. To save it, she
creates a small dialog window with a child package that asks for the
name of the new file. She can compile the smaller window independently
of the large one. If later she decides to make the name of the file
default to the day's date, then she can edit the child package and
recompile it as an independent entity, again without involving the
code for the large window. With Ada 83, the developer would have had
to recompile a monolithic system each time. Aside from slowing
compilation, it would have brought in thousands of functions that she
would not use.
In addition, the Claw helps to reduce the size of the developer's
application. In following good application development techniques, a
developer will strive to restrict herself to one kind of dialog box,
window type, etc. Having a wide variety of boxes or windows among
functions, such as dialog boxes of different sizes for saving files versus
opening files, distracts and confuses the user. But without owning
the code to Win32, Microsoft's Application Program Interface (API)
for both Windows 95 and Windows NT, the developer would be forced
to abandon the strong development technique and use many different
styles as she added functionality or to maintain one style at the cost
of greatly increased application size.
To give an example of the Claw's savings in application size, Brukardt
discussed the project's GUI builder, currently under development at
R.R. Software. The builder is being written in Microsoft Foundation
Classes (MFC) and C++ because, until they complete their own work, no
binding yet exists with which to develop it in Ada 95. The prototype
version, linked statically, was 1.6 MB-2 MB, without any functioning.
"It dragged in everything," Brukardt said. "It can't be using all that
code, but it is all in there, because it is all part of the MFC." The
prototype for the first cut at the bindings, on the other hand, was only
70K. While Brukardt admits that the comparison of the GUI prototype
builder and the prototype binding sample program is a bit like comparing
apples and oranges, it is still notable that the first is larger than
the second by a factor of 20.
Claw also has a default value for many parameters, such as window size
and colors, which further ease the Windows application developers' workload.
The environment assumes that system default sizes and colors will be used
for each function so that the developer does note have to specify size and
color with the addition of each new function.
Claw also allows developers to build the visual elements of the application
by drawing them on the screen: the developer draws the box and the software
generates new code for it. Previously, Ada programmers who did not
want to resort to a C code generator would have to create a dialog box,
for example, by counting the coordinates on the screen, compiling the whole
program, then checking the results and editing the numbers until they got it
right, often requiring several hours.
The Role of Object-Oriented Design (OOD)
Not only will the GUI help Ada programmers to use object-oriented
design, the binding itself is designed around objects. Brukardt asserts
that an OOD approach is the natural choice for GUIs.
Brukardt also chose OOD to avoid changing the underlying code that structures
the application. If he had used Ada 83 or C, every time he changed the custom
part of code, he would have had to change the driver for it, introducing
mistakes that would be hard to find.
For those using the Microsoft Windows 95 binding to program in
Ada, OOD allows the framework to insert its own code with minimal editing
to the code of the basic application. By declaring a single object, the
developer gets a blank tool bar and menu without any coding. For example,
the OOD allows him to change the menu handler without changing the resize
code if he did not want to, which is an inherent part of the GUI and should
work fine. In other words, the GUI binding looks like an application before
the developer does any coding at all; much like a standard form, the format
is provided, but the user fills in the content.
The Ada 95 Advantage
Ada 83, the original Ada, could have interfaced with Microsoft's new
operating system, but only with a colossal commitment of program
size and compilation time. According to Brukardt, Ada 95 can now
interface easily with Windows 95 because of
the language's new, standardized interface to C. It also allows Claw
to be ported to other compilers. R.R. Software has developed the
binding along an object-oriented design, which Brukardt says is a perfect
match for a user interface.
Ada 95 features many new characteristics that support object-oriented
design more strongly than did Ada 83. Ada was designed to facilitate
strong software engineering, which often encouraged an OO approach;
Ada 83, therefore, did offer some OO capabilities. Veteran Ada programmers
insist that inheritance support, for example, is not a feature that is new to the language
-- Ada 83's generics performed that function. In fact, since the
first release of the language, Ada has offered many C++ features: modularity,
packaging, etc. "Studies show that most C++ users really
use very little OOP," Brukardt said. "Ada has always offered exactly what
C programmers actually use in C++. They get the wonders of strong typing
and encapsulation, which they could have had 10 years ago if they had used Ada."
Ada 95, however, does offer many more fully object-oriented design features,
rather than just object-based.
Writing Windows 95 applications in Ada 95 may now be
easier than writing them in any other language because Claw
exploits many of Ada's new features. In addition to child packages,
Ada 95's inheritance is a "big advantage" in designing the GUI through
objects. Developers using the GUI for their own applications will exploit
the inheritance feature extensively, since the ability for types to
inherit the primitive operations of "ancestor types" is fundamental to OOP.
If types Heat and Smoke are derived from type Pollution, all three can be
added and subtracted from the previous day's figures without separate
declarations. Such an application would also bring in Ada 95's dynamic
binding, which allows the parameters of a type to be determined during
execution rather than during compile time, such the amount of Heat and Smoke
that Chimney #1 has emitted in the last hour.
Another Ada 95 innovation is returning errors via exceptions, finding the
right balance between ignoring unimportant glitches and warning the developer
when major problems arise. The Win32 binding returns a Boolean true or false
when checking for the existence of errors. A lot of the errors are extremely
rare or nonexistent, while others are crucial. C software will usually compile
no matter, which allows programmers to ignore errors -- sometimes wisely,
sometimes not.
Ada 83 bindings to Win32 returned every error as a function, which
the programmer had to read and do something about whether or not it was
important. With Claw, the error is turned into an Ada
program that returns an exception. Usually it does not raise an
exception and does not have a return, because the program treats it as
a procedure call. If an error does occur, then the program raises an
exception and handles it. If it is important, then the program aborts
and the programmer can handle the error while debugging it, instead
of during run-time. Along with the exception, the binding returns
error numbers that are part of Windows' exception message.
In Claw's object-oriented design, the R.R. developers have made extensive use
of one of Ada 95's five new reserved words, "tagged," which indicates a tagged
type, as well as Ada 95's type extension, inheritance, and polymorphism, all of which
are interrelated. A developer can add components to a tagged type derived
from an ancestor type. The derived type is an extension of the ancestor.
She can then define additional primitive subprograms, called dispatching
operations, and override others as part of the inheritance feature. The
software can call the dispatching operations statically through controlling
tags during compilation. It can also determine the controlling tag
dynamically -- at run-time, it determines the body to which the
call is dispatched. The controlling tag is determined through the properties
of the operands and context of a particular call on a dispatching operation.
In turn, that decides whether or not the call is a dispatching call. When the
programmer has a dispatching call call a dispatching operation, she has
achieved run-time polymorphism.
The Claw Mailing List
Those who are interested in receiving updates on Claw, may join R.R. Software's
Claw mailing list by sending an email message to
Claw-request@rrsoftware.com
Include in the body of the message: SUBSCRIBE
For more information via the Web, access R.R. Software's homepage for Claw at http://www.rrsoftware.com/claw.htm.
Ada Technology Insertion Program-Partnerships.
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