Chapter 17. Modules

Any fool can make things bigger, more complex, and more violent. It takes a touch of genius—and a lot of courage—to move in the opposite direction.

— Albert Einstein

Code reuse is a core best practice, and modules are Perl's principal large-scale mechanism for code reuse. They are also at the heart of Perl's greatest software asset: the CPAN.

Refactoring source code into modules will not only increase the reusability of that code, it is also likely to make the code cleaner[113] and easier to maintain. If nothing else, the programs from which the original code is removed will become shorter, better abstracted, and consequently more maintainable.

The keys to good module design and implementation are: designing the interface first, keeping that interface small and functional, using a standard implementation template, and not reinventing the wheel. The guidelines in this chapter explore these issues.


Design the module's interface first.

The most important aspect of any module is not how it implements the facilities it provides, but the way in which it provides those facilities in the first place. If the module's API is too awkward, or too complex, or too extensive, or too fragmented, or even just poorly named, developers will avoid using it. They'll write their own code instead.

In that way, a poorly designed module can actually reduce the overall maintainability of a system.

Designing module interfaces requires both experience ...

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