CHAPTER 3

Module Design and 

Implementation

P

ROGRAMMING IS BOTH

science and art. The last chapter equipped you with the science 

of modular programming in Perl the syntax and behavior of modules. This chapter 

will present the other side the art of designing and implementing modules.

Just by using modular programming you're ahead of the programming pack 

the majority of working programmers spend their days desperately writing one off 

scripts in a dialect of Perl akin to BASIC. That said, there are good modules and 

there are bad modules. This chapter will help you write modules that resemble the 

former more than the latter. I expect you to treat the advice given critically the 

best design technique to use will depend on your aesthetics, and that's the last 

thing I want to dictate!

Ultimately, there's only one inviolate rule of software design: Do it. It's worth it. 

The satisfaction you gain from jumping into the fray with some impulse coding 

won't last when the first wave of bug reports and unexpected changes lands. I'll 

leave it to the management books to break out the charts and graphs; if you give it 

a try you'll soon convince yourself. Every moment of thought and planning you 

put into a project at the outset will be paid back in spades by the end. It's a rare task 

that's really so small that it's worth knocking off without consideration.

Check Your Slack

Before you start a new module, you should visit CPAN.

1

 You may be able to avoid a 

lot of work (and thus gain a lot of slack) by reusing an existing module. If you need 

features that an existing module doesn't provide, consider extending the module. 

Object oriented modules can usually be extended through inheritance. If you 

make changes to a CPAN module, consider contributing those changes back to the 

author.

2

 Remember, one of the virtues of a Perl programmer is laziness; CPAN is 

the greatest enabler of programmer laziness since the terminal!

1. See Chapter 1 for copious instructions.

2. If you'll be distributing your module, then you may be required to release the source for any 

changes under the same license as the module. Be sure to read the license for the module 

before you start making modifications!

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