Conclusion

One might be tempted to suggest that the real problem with the Modem scenario is that the original designers got the design wrong. They should have known that connection and communication were separate concepts. Had they done a little more analysis, they would have found this and corrected it. So, it is tempting to blame the problem on insufficient analysis.

Poppycock! There is no such thing as enough analysis. No matter how much time you spend trying to figure out the perfect software structure, you will always find that the customer introduces a change that violates that structure.

There is no escape from this. There are no perfect structures. There are only structures that try to balance the current costs and benefits. Over time, those structures must change as the requirements of the system change. The trick to managing that change is to keep the system as simple and as flexible as possible.

The ADAPTER solution is simple and direct. It keeps all the dependencies pointing in the right direction, and it's very simple to implement. The BRIDGE solution is quite a bit more complex. I would not suggest embarking down that road until you had very strong evidence that you needed to completely separate the connection and communication policies and that you needed to add new connection policies.

The lesson here, as always, is that a pattern is something that comes with both costs and benefits. You should find yourself using the ones that best fit the problem at hand.