Perl Hacks

Hack #72. Find Functions Safely

Look for code to execute without risking explosions.

The ultimate goal of designing reusable code is genericity—being able to write useful pieces of code that allow future expansion without (much) difficulty or modification. Complete genericity is difficult, as your code has to make some assumptions somewhere.

Perl's very flexible about how you interact with other code. You can fold, spindle, mutilate, and mangle symbols in any package you want at almost any time. Although this flexibility makes it possible to find code in other packages, sometimes it makes it difficult to know if the function you want is really there, at least safely and without digging through symbol tables.

You can do it, though.

The Hack

If you can avoid the problem, avoid it.

One of the most common ways to interact with other code is to provide an interface you expect it to fulfill. This may be through suggesting that all plug-ins inherit from a base class that provides default methods to overload or through documenting that your code will always call plug-in methods and pass specified arguments.

Subclassing can be fragile, though, especially in Perl where your implementation choices affect everyone else who writes code. (See the implementation of HTTP::Daemon and how it stores instance data, for example.)

If you only need to know that plug-ins or extensions conform to an interface, consider using a Perl 6-ish module such as Class::Roles or Class::Trait. Though there's a little ...