Advanced Perl Programming

Chapter 1. Data References and Anonymous Storage

If I were meta-agnostic, I’d be confused over whether I’m agnostic or not — but I’m not quite sure if I feel that way; hence I must be meta-meta-agnostic (I guess).

—Douglas R. Hofstadter, Gödel, Escher, Bach

There are two aspects (among many) that distinguish toy programming languages from those used to build truly complex systems. The more robust languages have:

• The ability to dynamically allocate data structures without having to associate them with variable names. We refer to these as “anonymous” data structures.

• The ability to point to any data structure, independent of whether it is allocated dynamically or statically.

COBOL is the one true exception to this; it has been a huge commercial success in spite of lacking these features. But it is also why you’d balk at developing flight control systems in COBOL.

Consider the following statements that describe a far simpler problem: a family tree.

Marge is 23 years old and is married to John, 24.

Jason, John’s brother, is studying computer science at MIT. He is just 19.

Their parents, Mary and Robert, are both sixty and live in Florida.

Mary and Marge’s mother, Agnes, are childhood friends.

Do you find yourself mentally drawing a network with bubbles representing people and arrows representing relationships between them? Think of how you would conveniently represent this kind of information in your favorite programming language. If you were a C (or Algol, Pascal, or C++) programmer, you ...