Wednesday, April 11, 2007

TAS Must Die, Chapter 10b

I figured I'd goof off with the Decorator pattern. It didn't take long to find a more satisfying solution to the problems outlined previously.

The gist of the Decorator pattern is that you have potentially several classes each implementing some interface X. They each accept and X as an input stream. So you can daisy-chain them together as needed.

IntX t1 = new GetWords(); // GetWords implements IntX
IntX t2 = new Trim(t1); // Trim implements IntX
IntX t3 = new Upper(t2); // Upper implements IntX
private void loop(IntX q)

So as we buzz in the while loop, we read from t3, t3 reads from t2, and t2 from t1. I don't know where t1 gets its input :-) Assume t1 returns " now". t2 trims it to "now". t3 converts it to "NOW". So the loop prints trimmed uppercase words. If you decided you needed to enhance this to produce German, you could create a new IntX decorator that sipped from t3 and performed the translation. A nice thing about this is that you can reorder the IntX's (sometimes it matters), add new ones, or remove some, without any negative impact on your code. Note that the loop accepts the IntX interface - it has absolutely no clue what's going on behind the scenes in "q". That's a good thing.

So, thumbs up for the decorator pattern.

Later I'll talk about another nice pattern, the Visitor. This decouples the navigation in the NFA from some action to do on those states.

No comments:

Post a Comment