Contributor: JOHN GOHDE
TOPIC : Cool stuff Borland left out of their TP manuals. ;-)
FOR : TP 4.0+
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This post is about cool programming concepts that will be
referred to either directly or indirectly in my ON PASCAL ...
tutorial series of messages.
The underlying programming style that will be implemented in my
posts is called OBP, Object Based Programming, or Modular
Programming. This programming style provides many of the benefits
of Object Oriented Programming (OOP) without actually having to
use OOP code in your programs.
These benefits are namely: 1)the ability to manage complexity in
your programs, 2)easy to use reusable object code in the form of
TPUs, and 3)fewer program bugs. Further, you are able to stick
with traditional programming methods with OBP.
The following are definitions of cool programming concepts. You
are going to have to accept on faith that these are NOT just
boring definitions!!! Every time you write a program you should
be thinking about and using this cool stuff. As Borland does not
talk about them in the context of OBP, I will. ;-)
So, ... It is time to rattle your brains a little.
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ABSTRACTION
-----------
It is the process by which programmers distill the essential
characteristics of some conception that distinguishes it from all
others. Abstraction is why High Level Programming Languages (HLL)
were invented! HLLs achieve abstraction by allowing programmers
to write programs without having to bit-twiddle. Bit-twiddling is
for Assembly Programming. Every HLL implements abstraction to a
certain degree. Hence, bit-twiddlers should stay with ASM, and
everybody else should start thinking in terms of abstraction
rather than bit-twiddling in their programs!!! ;-)
ABSTRACT DATA TYPE (ADT)
------------------------
A data type that is defined in terms of the operations that can
be performed on objects of that type rather than by the
properties of the objects themselves. ADTs represent an
intermediate step between traditional programming and
object-oriented programming. Among the many cool uses of ADTs,
they can make your code portable. Think of ADTs as the ultimate
level of abstraction in high level programming.
BINDING TIME
------------
The point in a program at which reference to a program's elements
or abstractions are bound to specific computer's storage
locations and values.
BLOCK
-----
A block is a segment of source code that can be selected and
acted upon as a whole. Think of blocks as being a relative level
of abstraction.
CAST
COERCION
--------
A data conversion from one type to another. They are used to
selectively turn off type checking in TP.
DATA TYPE
---------
A definition of a set of data that specifies the possible range
of values of the set, the operations that can be performed on the
values, and the way in which the values are stored in memory. The
concept of a data type makes data manipulation more abstract and
hides the underlying binary representation of the data. We will
be using Modules to implement Data Types in TP. Think of data
types instead of just types as they are the total package!!!
DYNAMIC BINDING
LATE BINDING
---------------
Binding that occurs during program execution. We will achieve to
a degree this type of binding with traditional programming
methods using procedural types and pointers.
GLOBAL VARIABLE
---------------
A variable whose value can be accessed and modified by any
statement in a program. These variables exist during the entire
time a program executes. Conventional wisdom is that Global
variables are to be avoided as they can easily result in side
effects.
INFORMATION HIDING
------------------
A design practise in which implementation details for both data
structures and algorithms within a module are hidden from
routines using same. What is hidden does not contribute to the
essential characteristics of the abstraction. In theory, it
allows you to use modules in a manner different from the planned
way without breaking the routine that calls it. In short units,
modules, and routines are supposed to give out information on a
need to know basis only, in order to avoid side effects.
LOCAL VARIABLE
--------------
A program variable whose scope in TP is limited to a given block
of code or routine. These variables exist only while the given
routine is executing. Conventional wisdom is that you should use
Local rather than Global variables in your program.
MODULAR DESIGN
--------------
An approach to software design in which a program is broken down
into small units, or modules, each of which can be developed,
tested, and finished independently before being combined with
other modules.
MODULAR VARIABLE
----------------
A conceptual subset of global variables. They exist during the
entire length of program execution but can be accessed and
modified ONLY by a block of code known as a module. They are to
be considered good global. In TP, we will be implementing Modular
variables with OBP. You will need to use these since it is
impractical to avoid all use of global variables.
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MODULE
------
A collection of routines and data structures that performs a
particular task or implements a particular abstract data type. We
will implement modules in TP as a conceptual block of related
units.
OBJECT BASED PROGRAMMING (OBP)
MODULAR PROGRAMMING
------------------------------
A precursor of object-oriented programming in which the program
is broken down into several independently compiled modules. It is
considered a refinement of structured programming or traditional
programming methods. OBP recognizes the strong role that data
plays in programs.
PASCAL
------
A programming language designed to encourage programmers to write
modular and well structured programs. With Pascal the programmer
is supposed to deal with abstractions rather than always working
directly with computer memory. Pascal was designed for those
programmers who want the highest levels of abstraction possible
in their programs. Did you know that? ;-)
SIDE EFFECT
-----------
An unanticipated effect or change of state caused by a routine
that happens when the program is executed. In other words, they
are program "bugs".
STATIC BINDING
EARLY BINDING
--------------
Binding that occurs during program compilation or linkage. This
is the binding used with traditional programming methods.
STRONG TYPING
-------------
A characteristic of Pascal that does not allow the program to
change the type of a variable during program execution.
STRUCTURED PROGRAMMING (SP)
TRADITIONAL PROGRAMMING METHODS
-------------------------------
A style of programming designed to make programs more
comprehensible and programming errors less frequent. Strictly
speaking, SP concentrates on algorithms or flow of control while
neglecting the role of data or objects.
TYPE
----
Defines the nature of a variable. It is a level of abstraction.
TYPE CHECKING
-------------
The examination by a compiler of the operations in a program to
make sure that the operations make sense, that the correct data
types are being used, and that all expressions are guaranteed to
be type-consistent.
VISIBILITY
SCOPE OF ...
-----------
This refers to the extent a given identifier can be referenced in
a program. Another way of looking at this issue is how long does
an identifier in a program exist.
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