Shipman's software books: Design patterns

Gamma, Erich, et al. Design patterns. Addison-Wesley, October 1995, ISBN 0201633612.

This is not a work for beginners, and not an easy one. I would recommend it, however, to anyone who has done some fair-sized software projects (say, over 5,000 lines of code), and especially those who have mastered the basics of object-oriented programming.

The writers provide an excellent new high-level look at proper organization of large programs. Basing their work on Christopher Alexander's seminal work in the architecture of buildings, they have identified some higher forms of organization that can be useful in your higher-order design work.

For example, I've gotten a lot of mileage out of what they call the Singleton pattern. Sometimes you build a class that really should only be instantiated once. Here are some examples from my work:

• Many programs I write can generate a lot of nonfatal error messages. I prefer that programs have the option of logging all such messages into a file, as well as writing them to the standard output stream. I wrote a Log object (first in Icon, later in Python), that centralizes this logging. Any segment of code that needs to send an error message can instantiate this Log object, but they will all share the same instance. This means that the object doesn't have to be a global and it doesn't have to get passed to every routine that uses it. (See my cleanroom object library for source code.)
• I wrote some Python objects that sit on top of the Python universal database interface. The various supported interfaces generally support any number of operations from a single connection to the server, and for performance reasons it is best to use only a single connection. My `TheDatabase' class can be instantiated any number of places in the program, but they all use the same connection object.

I've used several of the other patterns too, such as Factory.

Like a lot of the best software books, this is not light reading, but it's worth the effort.

Last updated: 1999/05/09 18:48:07
URL: http://www.nmt.edu/~shipman/reading/gamma.html