“A Conversation with Martin Fowler”

Bill Venners interviewed Martin Fowler back in 2002 that resulted in six part series filled with engineering wisdom to absorb.

Among the many exchanges was the following on flexibility that reinforces some principals I try (not always successfully) to put in practice:

Bill Venners: In Refactoring you write, “Before I used refactoring I always looked for flexible solutions. Because design changes were expensive, I would look to build a design that would stand up to changes I could forsee. The problem with building a flexible design is that flexibility costs.” What is the cost and what is the alternative?

Martin Fowler: The cost of flexibility is complexity. Every time you put extra stuff into your code to make it more flexible, you are usually adding more complexity. If your guess about the flexibility needs of your software is correct, then you are ahead of the game. You’ve gained. But if you get it wrong, you’ve only added complexity that makes it more difficult to change your software. You’re obviously not getting the payback.

It’s not hard to guess wrong about flexibility needs. You can guess wrong if requirements change. What you think is a requirement for flexibility now may go away or change in the future. You can also guess wrong if you put extra code into the program to improve flexibility but you don’t get it quite right. You get more complexity without getting the flexibility you were after.

The alternative is to use the XP approach and not put the flexibility in at all. XP says, since most of the time we get it wrong, just don’t put the flexibility in there. Now if you can’t evolve your design safely, then that is a foolish route to take. But if you can evolve your design safely, it becomes quite a nice approach. In fact it becomes a self-reinforcing approach. If you strive to keep your design as simple as possible by avoiding speculative flexibility, then it’s easier to change the code because you have less complication to deal with. The code is easier to understand and easier to change. As a result, you can make changes much more quickly.

Read the whole series:

Refactoring with Martin Fowler

Design Principles and Code Ownership

Evolutionary Design

Flexibility and Complexity

Test-Driven Development

Tuning Performance and Process