5 - Forth Interest Group

O& je c t - Orien t e d
Forth
"
/ New Westminster, British Columbia, Canada
I
yourself, but you should
protect your code from what
those other crazy, reckless,
undisciplined hacks might
do. It is possible to de-couple
to the extent of not even
allowing dired reference to
a data type's routines. In-
stead, a message is sent over
to that module asking for a
procedure to be enacted.
Thus, even the data type's
procedures could be modihed
(which might be necessarv
if the details of the data
change), and still it would
not affect any other module.
1
1
n the beginning, there was tion that a routine should do twoflmt-t~~evariablescalled The intent here is to provide
programming. Now, the one thing and only one thing REAL and IMAGINARY) that robust code by limiting side
programming was form- (and do it well). However, data abstraction is important. of changes, and to
less and unstructured- there was more to be discov- A procedure's code is ~~~- provide reusable code by
darkness was over the sur- ered.
saril~s~ecificaboutwhatt~~e de-coupling it from as much
face of the design problem. If a careful study of pro- of data it operates upon. The as possible.
Then came structured cedures proved beneficial, code of + (plus) assumes an The intent of object-oriprogramminpa
disciplined then what about a close look integer data type, and F+ (f- ented programming is to
coding style and a logical at the nature and form of the ~lus)assmesafloating-~int extend the ideas of strucanalysis
technique which data being operated upon data type. These cannot be tured programming to inemphasized
the nature of by those newly-structured swapped (or even duped-- clude techniques dealing
the coupling between code routines? Thus, someone else Your employment may with data which enhance
modules and the design coined the phrase object be over). Thus, it only makes reliability and minireasons
behind the creation o&nW, probably in con- sense to group the definition mize the maintenance of a
of the code modules. Creat- trast to the prevailing proce- of a data type with each and software project by reducing
ing a routine out of code that dure-oriented programming every procedure that will the amount of modifications
just happened to be per- of the time.
operateu~onit-makingfor necessitated by a change.
formed at the same time
easier maintenance. When a
(temporal cohesion) was out
Enter Analysis of Data
data type's definition and its
Glossary
Creating one routine out of
Data canbe kept in atomic
associated procedures are In the object-oriented
code that did a couple of
types like variables, congrouped
into one module, vernacular, a data structure
closely related things Oogistants,
and literals; or in
furtherde-couplingbetween is called an object or an incal
cohesion) was out-it
molecular groupings, such
modules can be realized. For stance of a class. The class
necessitated passing control
as named records and inexample,
a stack can be contains the information
flags between routines (called
dexed arrays. Many early
implemented using an in- necessary to construct an
control coupling, oddly
computer languages prodexed
array, or a buffer and instance, as well as all the
enough). There was (once
vided a small selection of
an offset. Allowing any other routines that operate on its
, again?) the dawning realizaatomic
data types and exmodule
to know the imple- data type. The internal obmentation
details is not nec- jects that make up an inessary
and could allow di- stance Oike fields within a
information hiding is the back= rect aces to elements within record) are called instance
bone of code security, reliable the stack structure. This di- variables. An object is sent a
red access is a potential message, which specifies
re-entrancy, and data abstraction problem for the future, if what to do, but not how to
ever the implementation of do it. The object then finds
( pected you to use records, stack structure is changed. the method the word that
1 for example, to simulate any "What they don't know can't performs the correct action;
Roger Bicknell is an electrical engi- different 'types of data hurt you." Of course, it is
neer who has programmed in Forth as
this is called binding the
might fancy. The ability to
a hobby since 1982. He enjoys the
important to keep in mind message to the object. There
simplicity and interactivity of the b- abstract data, or to create a that considerations like are two forms: earlybinding
guage, and uses it to experiment with new data type, is an essential maintenance are far more
language &sign. He says, 'Some
and late (or dynamic) bindfeature
of ah &ject-oriented
people gamble, I program ... Yes, I
complex and important for a ing. Early binding is done at
know it's 4:00 a.m., but I've just got to language
large multi-programmer compile time and dynamic
tweak this one last word ..." Row But it is not sim~lv for the project than for a lone-wolf, binding is done at run time.
welcomes feedback at 315 D&O~ prettiness of beiigdable to
Street. New Westminster, BC, Canada
one-nighter program. You The ability of one class to
V3L 4E8 or at R.BICKNELL2 on GEnie. refer a new data type like needn't hide anything from gain access to another class's
COMPLEX (say, made up of
Forth Dimensions 23 January 1992 February