Do we build code, or grow it? I was fortunate enough to attend a Michael Feathers workshop called Symbiotic Design earlier in the year, organized by the good people at Agile Singapore, where he is ploughing biological and psychological sources for ideas on how to manage codebases. There’s also some links to Naur and Simondon’s ideas on technical objects and programming that weren’t in the workshop but are meanderings of mine.
Feathers literally wrote the book on legacy code, and he’s worked extensively on techniques for improving the design of code at the line of code level. Other days in the week focused on those How techniques; this session was about why codebases change the way they do (ie often decaying), and techniques for managing the structures of a large codebase. He was pretty clear these ideas were still a work in progress for him, but they are already pretty rich sources of inspiration.
I found the workshop flowed from two organizing concepts: that a codebase is an organic-like system that needs conscious gardening, and Melvin Conway’s observation that the communication structure of an organization determines the shape of the systems its people design and maintain (Conway’s Law). The codebase and the organization are the symbionts of the workshop title. Some slides from an earlier session give the general flavour.
Feathers has used biological metaphors before, like in the intro to Working Effectively With Legacy Code:
You can start to grow areas of very good high-quality code in legacy code bases, but don’t be surprised if some of the steps you take to make changes involve making some code slightly uglier. This work is like surgery. We have to make incisions, and we have to move through the guts and suspend some aesthetic judgment. Could this patient’s major organs and viscera be better than they are? Yes. So do we just forget about his immediate problem, sew him up again, and tell him to eat right and train for a marathon? We could, but what we really need to do is take the patient as he is, fix what’s wrong, and move him to a healthier state.
The symbiotic design perspective sheds light on arguments like feature teams versus component teams. Feature teams are a new best practice, and for good reasons – they eliminate queuing between teams, work against narrow specialization, and promote a user or whole-product view over a component view. They do this by establishing the codebase as a commons shared by many feature teams. So one great question raised is “how large can the commons of a healthy codebase be?” Eg there is a well known economic effect of the tragedy of the commons, and a complex history of the enclosure movement behind it. I found it easy to think of examples from my work where I had seen changes made in an essentially extractive or short-term way that degraded a common codebase. How might this relate to human social dynamics, effects like Dunbar’s number? Presumably it takes a village to raise a codebase.
Feathers didn’t pretend to have precise answers when as a profession we are just starting to ask these questions, but he did say he thought it could vary wildly based on the context of a particular project. In fact that particularity and skepticism of top down solutions kept coming up as part of his approach in general, and it definitely appeals to my own anti-high-modernist tendency. I think of it in terms of the developers’ theory of the codebase, because as Naur said, programming is theory building. How large a codebase can you have a deep understanding of? Beyond that point is where risks of hacks are high, and people need help to navigate and design in a healthy way.
((You could, perhaps, view Conway’s Law through the lens of Michel Foucault, also writing around 1968: the communication lines of the organization become a historical a priori for the system it produces, so developers promulgate that structure without discussing it explicitly. That discussion deserves space of its own.))
Coming back to feature teams, not because the whole workshop was about that, but because it’s a great example, if you accept an organizational limit on codebase size, this makes feature/component teams a spectrum, not good vs evil. You might even, Feathers suggests, strategically create a component team, to help create an architectural boundary. After all, you are inevitably going to impact systems with your organizational design. You may as well do it consciously.
A discussion point was a recent reaction to all of these dynamics, the microservices approach, of radically shrinking the size of system codebases, multiplying their number and decentralizing their governance. If one component needs changes, the cost of understanding it is not large, and you can, according to proponents, just rewrite it. The organizational complement of this is Fred George’s programmer anarchy (video). At first listen, it sounds like a senior manager read the old Politics Oriented Software Development article and then went nuts with an organizational machete. I suspect that where that can work, it probably works pretty well, and where it can’t, you get mediocre programmers rewriting stuff for kicks while the business paying them drowns in a pool of its own blood.
Another architectural approach discussed was following an explicitly evolutionary approach of progressively splitting a codebase as it grew. This is a technique Feathers has used in anger, with the obvious biological metaphors being cell meiosis and mitosis, or jellyfish reproduction.
The focus on codebases and the teams who work on them brings me back to Gilbert Simondon’s idea of the “theatre of reciprocal causality”. Simondon notes that technical objects’ design improvements have to be imagined as if from the future. They don’t evolve in a pure Darwinian sense of random mutations being winnowed down by environmental survival. Instead, when they improve, especially when they improve by simplification and improved interaction of their components, they do so by steps towards a potential future design, which after the steps are executed, they become. This is described in the somewhat mindbending terms of the potential shape of the future design exerting a reverse causal influence on the present: hence the components interact in a “theatre of reciprocal causality”.
This is exactly what programmers do when they refactor legacy code. Maybe you see some copy-pasted boilerplate in four or five places in a class. So you extract it as a method, add some unit tests, and clean up the original callers. You delete some commented out code. Then you notice that the new method is dealing with a concept you’ve seen somewhere else in the codebase. There’s a shared concept there, maybe an existing class, or maybe a new class that needs to exist, that will tie the different parts of the system together better.
That’s the theatre of reciprocal causality. The future class calling itself into existence.
So, given the symbiosis between organization and codebase, the question is, who and what is in the theatre? Which components and which people? Those are the components that have the chance to evolve together into improved forms. If it gets too large, it’s a stadium where no one knows what’s going on, one team is filming a reality TV show about teddy bears and another one is trying to stage a production of The Monkey King Wreaks Havoc In Heaven. One of the things I’ve seen with making the theatre very small, like some sort of Edinburgh Fringe Festival production with an audience of two in the back of an old Ford Cortina, is you keep that component understandable, but cut off its chance at technical evolution and improvement and consolidation. I’m not sure how that works with microservices. Perhaps the evolution happens through other channels: feature teams working on both sides of a service API, or on opportunistically shared libraries. Or perhaps teams in developer anarchy rewrite so fast they can discard technical evolution. Breeding is such a drag when drivethru immaculate conception is available at bargain basement prices.