…which was, and is, a hugely important part of our software development, and something that took a long time to learn to do well.

Pair programming is when two developers sit at one machine and one keyboard to write the software. It’s very difficult to do: the driver has the pressure of someone watching their every move, and the navigator has to be aware of what’s going on because they’ll be asked to take over at any moment and they have a responsibility to keep an eye on the bigger picture. It also makes it a very collaborative process — the pair need to work out together exactly how they’re going to tackle every problem. Mat, leading our architecture team, calls this “keeping each other honest”.

Pairing looks expensive — two people apparently doing something that one could do — but that makes the mistake of thinking that all software is the same and all developers are interchangeable. Here are some of the benefits we’ve found:

• Developers are more productive. With someone sitting beside you you can’t afford to cruise. You’ve got to be demonstrably on the ball all the time.
• The quality of the software is much higher. I’ve listened to developers discussing how they should write a particular piece of code, suggesting alternatives and weighing up pros and cons that one individual would never have come up with by themselves.
• Developers become much more skilled much more quickly. Everyone learns off everyone else.
• The company’s technology investment is de-risked. Highly specialised knowledge is shared among many people, and doesn’t live just in the head of one person. This also means…
• …Resourcing projects is easier. Because more people are able to move onto other teams more often, since (a) they are more likely to have the knowledge needed for the new team, and (b) they are less tied to their existing team since they will have shared that knowledge. This last point also means…
• …Developers have more opportunities to learn new things. They can move onto other teams and new projects, safe that they won’t be constantly called back to their previous team, because they’ll have shared their skills and knowledge.

When a software project is complete the software itself is only just beginning its life, in operation day after day — and in the case of our software, by hundreds of people for many years to come. So that development investment has to ensure the product is of very high quality, and pair programming is part of how we ensure that.