Perl Hacks

Hack #85. Replace Soft References with Real Ones

Combine the benefits of name-based references, lexicals, and typo-checking.

One of the first milestones in becoming an effective programmer is the sudden flash of Zen when you first ask the question "How can I use a variable as a variable name?"^[2] The second half of that zap of enlightenment is when you realize why you usually don't need to do that.

Sometimes it's the easiest solution to a problem, though—especially when you're refactoring a large, complex piece of code written by someone who just didn't get it yet.

Don't despair; you can have all of the benefits with almost none of the drawbacks.

Suppose you have a sales reporting application such as one the author had to maintain many lives ago. There are multiple types of items for sale, each with its own separate total in the report. You have a parser that reads external data, giving you a key-value pair with the name of the sale category and the value of the item.

Unfortunately, the program uses several lexical-but-file-global variables and you don't have time to change the whole thing to use an obvious %totals hash.

Tip

If that's not scary enough, imagine that the actual system really did use symbolic references here (yes, that implies globals, not lexicals!) without error checking and that the sales totals came from the Internet through unencrypted means. Suddenly being a writer seems appealing.

The code, minus the section you need to change and with a fake data-reading section ...