A few comments:
  1. I'm merely pointing out that no data structure can prevent the scenerio you describe.

    No, but it can mitigate it. I am saying that, all things being equal, nested data structures contain more information intrinsic to their structure that parallel ones do.

  2. Will the programmer know to look in $$object{ISBN} for the piece of data he needs to fulfill the change request?

    Yes, he/she will. Why? Because they can go look at the definition for $object and see that there is an ISBN member. (You do have object definitions, right?) Failing that, Data::Dumper is one of the maintenance programmer's best friends. But, Data::Dumper doesn't know about that parallel data structure, does it? If it doesn't, it takes more time for me to find the right solution.

    (Nit: Use $object->{ISBN} instead ... $$object{ISBN} can lead to subtle bugs. Another maintenance headache, not a style issue.)

  3. The program will get the same result either way.

    This is a horrible statement, especially in this argument. Not only is it a tautology, but I don't care what hoops the computer has to go through to understand what I want it to do. COMPUTER RESOURCES ARE (NEARLY ALWAYS) CHEAPER THAN HUMAN RESOURCES.

Let me put that last point another way. My programming services cost more per week than a top-of-the-line linux server. People like merlyn and others cost at least twice that. Is it worth it to you for me to spend 40 hours figuring out how to save a meg of RAM?

It is worth a lot of money to write code that encapsulates as much information as possible in as many ways as possible that will be guaranteed to change as the code changes. Parallel data structures are a matter of style, yes. They are a poor choice of style because they will cost more money in maintenance than nested structures.

------
We are the carpenters and bricklayers of the Information Age.

Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

In reply to Re2: Parallel structures are NOT maintainable by dragonchild
in thread using references as keys in a hash. by habit_forming

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