OOP the Easy Way

It’s still very much a work in progress, but OOP the Easy Way is now available to purchase from Leanpub (a free sample is also available from the book’s Leanpub page). Following the theme of my conference talks and blog posts over the last few years, OOP the Easy Way starts with an Antithesis, examining the accidental complexity that has been accumulating under the banner of Object-Oriented Programming for nearly four decades. This will be followed by a Thesis, constructing a model of software objects from the essential core, then a Synthesis, investigating problems that remain unsolved and directions that remain unexplored.

At this early stage, your feedback on the book is very much welcome and will help yourself and fellow readers to get more from the book. You will automatically get updates for free as they are published through Leanpub.

I hope you enjoy OOP the Easy Way!

Recommend me some books or articles

I’ve been looking for something to read on these topics, can you help?

  • a history of the Unix wars (the ‘workstation’ period involving Sun, HP, Apollo, DEC, IBM, NeXT and SGI primarily, but really everything starting from AT&T up to Linux and OS X would be interesting)
  • a business case study on Apple’s turnaround 1997-2001. I’ve read plenty of 1990s case studies explaining why they’ll fail, and 2010s interpretations of why they’re dominant, and Gil Amelio’s “On the Firing Line” which explains his view of how he stemmed the bleeding, but would like to fill in the gaps: particularly the changes from Dec 1997 to the iPod.
  • a technical book on Mach (it doesn’t need to still be in print, I’ll try to track it down): I’ve read the source code for xnu, GNU Mach and mkLinux, Tevanien’s papers, and the Mac OS X Internals book, but could still do with more

On books

I’d say that if there’s one easy way to summarise how I work, it’s as an information focus. I’m not great at following a solution all the way to the bitter end so you should never let me be a programmer (ahem): when all that’s left is the second 90% of the effort in fixing the bugs, tidying up edge cases and iterating on the interaction, I’m already bored and looking for the next thing. Where I’m good is where there’s a big problem to solve, and I can draw analogies with things I’ve seen before and come up with the “maybe we should try this” suggestions.

Part of the input for that is the experience of working in lots of different contexts, and studying for a few different subjects. A lot of it comes from reading: my goodreads account lists 870 books and audiobooks that I’ve read and I know it to be an incomplete record. Here are a few that I think have been particularly helpful (professionally speaking, anyway).

  • Douglas Adams, The Hitch-Hikers’ Guide to the Galaxy. Adams is someone who reminds us not to take the trappings of society too seriously, and to question whether what we’re doing is really necessary. Are digital watches really a neat idea? Also an honourable mention to the Dirk Gently novels for introducing the fundamental interconnectedness of all things.
  • Steve Jackson and Ian Livingstone, The Warlock of Firetop Mountain. I can think of at least three software projects that I’ve been able to implement and describe as analogies to the choose your own adventure style of book.
  • David Allen, Getting Things Done, because quite often it feels like there’s too much to do.
  • Douglas Hofstadter, Godel, Escher, Bach: An Eternal Golden Braid is a book about looking for the patterns and connections in things.
  • Victor Papanek, Design for the Real World, for reminding us of the people who are going to have to put up with the consequences of the things we create.
  • Donald Broadbent, Perception and Communication, for being the first person to systematically explore that topic.
  • Steven Hawking, A Brief History of Time, showing us how to make complex topics accessible.
  • Roger Penrose, The Road to Reality, showing us how to make complex topics comprehensively presentable.
  • Douglas Coupland, Microserfs, for poking fun at things I took seriously.
  • Janet Abbate, Recoding Gender, because computering is more accessible to me than to others for no good reason.
  • Joshua Bloch, Effective Java, Second Edition, for showing that part of the inaccessibility is a house of cards of unsuitable models with complex workarounds, and that programmers are people who delight in knowing, not addressing, the workarounds.
  • Michael Feathers, Working Effectively with Legacy Code, the one book every programmer should read.
  • Steve Krug, Don’t make me think!, a book about the necessity of removing exploration and uncertainty from computer interaction.
  • Seymour Papert, Mindstorms, a book about the necessity of introducing exploration and uncertainty into computer interaction.
  • Richard Stallman, Free as in Freedom 2.0, for suggesting that we should let other people choose between ther previous two options.
  • Brad Cox, Object-Oriented Programming: An Evolutionary Approach, for succinctly and effortlessly explaining objects a whole decade before everybody else got confused by whether a dog is an animal or a square is a rectangle.
  • Gregor Kiczales, Jim des Rivieres, and Daniel G. Bobrow, The Art of the Metaobject Protocol showed me that OOP is just one way to do OOP, and that functional programming is the same thing.
  • Simson Garfinkel and Michael Mahoney, NEXTSTEP Programming: Step One was where I learnt to create software more worthwhile than a page of BASIC instructions.
  • Gil Amelio, On the Firing Line: My 500 Days at Apple shows that the successful business wouldn’t be here if someone hadn’t managed the unsuccessful business first.

There were probably others.

Working Effectively with Legacy Code

I gave a talk to my team at ARM today on Working Effectively with Legacy Code by Michael Feathers. Here are some notes I made in preparation, which are somewhat related to the talk I gave.

This may be the most important book a software developer can
read. Why? Because if you don’t, then you’re part of the problem.

It’s obviously a lot easier and a lot more enjoyable to work on
greenfield projects all the time. You get to choose this week’s
favourite technologies and tools, put things together in the ways that
suit you now, and make progress because, well anything is progress
when there’s nothing there already. But throwing away an existing
system and starting from scratch makes it easy to throw away the
lessons learned in developing that system. It may be ugly, and patched
up all over the place, but that’s because each of those patches was
needed. They each represent something we learned about the product
after we thought we were done.

The new system is much more likely to look good from the developer’s
, but what about the users’? Do they want to pay again
for development of a new system when they already have one that mostly
works? Do they want to learn again how to use the software? We have
this strange introspective notion that professionalism in software
development means things that make code look good to other coders:
Clean Code, “well-crafted” code. But we should also have some
responsibility to those people who depend on us and who pay our way,
and that might mean taking the decision to fix the mostly-working

A digression: Lehman’s Laws

Manny Lehman identified three different categories of software system:
those that are exactly specified, those that implement
well-understood procedures, and those that are influenced by the
environment in which they run. Most software (including ours) comes
into that last category, and as the environment changes so must the
software, even if there were no (known) problems with it at an earlier
point in its evolution.

He expressed
Laws governing the evolution of software systems,
which govern how the requirements for new development are in conflict
with the forces that slow down maintenance of existing systems. I’ll
not reproduce the full list here, but for example on the one hand the
functionality of the system must grow over time to provide user
satisfaction, while at the same time the complexity will increase and
perceived quality will decline unless it is actively maintained.

Legacy Code

Michael Feather’s definition of legacy code is code without tests. I’m
going to be a bit picky here: rather than saying that legacy code is
code with no tests, I’m going to say that it’s code with
insufficient tests
. If I make a change, can I be confident that I’ll
discover the ramifications of that change?

If not, then it’ll slow me down. I even sometimes discard changes
entirely, because I decide the cost of working out whether my change
has broken anything outweighs the interest I have in seeing the change
make it into the codebase.

Feathers refers to the tests as a “software vice”. They clamp the
software into place, so that you can have more control when you’re
working on it. Tests aren’t the only tools that do this: assertions
(and particularly Design by Contract) also help pin down the software.

How do I test untested code?

The apparent way forward then when dealing with legacy code is to
understand its behaviour and encapsulate that in a collection of unit
tests. Unfortunately, it’s likely to be difficult to write unit tests
for legacy code, because it’s all tightly coupled, has weird and
unexpected dependencies, and is hard to understand. So there’s a
catch-22: I need to make tests before I make changes, but I need to
make changes before I can make tests.


Almost the entire book is about resolving that dilemma, and contains a
collection of patterns and techniques to help you make low-risk
changes to make the code more testable, so you can introduce the tests
that will help you make the high-risk changes. His algorithm is:

  1. identify the “change points”, the things that need modifying to
    make the change you have to make.
  2. find the “test points”, the places around the change points where
    you need to add tests.
  3. break dependencies.
  4. write the tests.
  5. make the changes.

The overarching model for breaking dependencies is the “seam”. It’s a
place where you can change the behaviour of some code you want to
test, without having to change the code under test itself. Some examples:

  • you could introduce a constructor argument to inject an object
    rather than using a global variable
  • you could add a layer of indirection between a method and a
    framework class it uses, to replace that framework class with a
    test double
  • you could use the C preprocessor to redefine a function call to use
    a different function
  • you can break an uncohesive class into two classes that collaborate
    over an interface, to replace one of the classes in your tests

Understanding the code

The important point is that whatever you, or someone else, thinks
the behaviour of the code should be, actually your customers have paid
for the behaviour that’s actually there and so that (modulo bugs) is
the thing you should preserve.

The book contains techniques to help you understand the existing code
so that you can get those tests written in the first place, and even
find the change points. Scratch refactoring is one technique: look
at the code, change it, move bits out that you think represent
cohesive functions, delete code that’s probably unused, make notes in
comments…then just discard all of those changes. This is like Fred
Brooks’s recommendation to “plan to throw one away”, you can take what
you learned from those notes and refactorings and go in again with a
more structured approach.

Sketching is another technique recommended in the book. You can draw
diagrams of how different modules or objects collaborate, and
particularly draw networks of what parts of the system will be
affected by changes in the part you’re looking at.

New book: APPosite Concerns

Back when I published APPropriate Behaviour, I expected it to be the first in a trilogy. Today, the second part, APPosite Concerns, is available.

APPosite Concerns is a compendium of posts from this blog, going back over the current decade. The main topics covered are being a programmer, designing software, thinking about software and computer systems, and software freedom. I hope you enjoy it, find it useful, or maybe even both.

Staying power

You would imagine that by now I would have come to realise how long my attention span is and worked to find projects that fit within it, but no. This is one of the changes I need to make soon.

So often I start a project really excited by it, but am really excited by something else before the end. Book projects always work that way, and quite a few software projects. Sometimes even talks, given a long enough lead time between being asked for a topic and actually giving the talk.

The usual result is that I become distracted before the end of the project, which leads to procrastination. That then makes it take longer, which only increases the distraction and disengagement.

What I’m saying is that if I ever say that I’m thinking of starting a PhD, you have my permission to chastise me. Four years is not within my observed boredom limit. Six months is closer to the mark.

The Design of the Bazaar

In The Design of Design, Fred Brooks makes an interesting point about ESR’s description of the Bazaar model of Linux (and, by extension, “Open Source”) development.

Linux was actually designed in a cathedral. The design was supplied by Unix, where Linux was to be a work-alike replacement for a particular component. There was even a functional specification: the GNU utilities already existed and the kernel had to support them.

APPosite Concerns

I’ve started another book project: APPosite Concerns is in the same series as, and is somehow a sequel to, APPropriate Behaviour. So now I just have one question to ask.

What is going to be in the book?

This question is easy to answer in broad terms. My mental conception of who I am and how I make software is undergoing a Narsil-like transformation: it has been broken and is currently being remade.

APPropriate Behaviour was a result of the build-up of stresses that led to it being broken. As I became less and less satisfied with the way in which I made software, I explored higher and higher levels looking for meaning. Finally, I was asking the (pseudo-)profound questions: what is behind software development? How does one philosophise about it? What does it mean?

If APPropriate Behaviour is the ascent, then APPosite Concerns is an exploration of the peak. It’s an exploration of what we find when nothing is worth believing in, of the questions we ask when there is really no understanding of what the answers might be.

It’s clear to me that plenty of the essays in this blog are relevant to this exploration, but of course there’s not much point writing a book that’s just some articles culled from my blog. There needs to be, if you’ll excuse a trip into the world of self-important businessperson vocabulary for a second, some value add.

I’ve written loads recently. As I said right here, I write a lot at the moment. I write to get ideas out of my brain, so that I can ignore them and move on to other ideas. Or so that I can get to sleep. I write on a 1950s typewriter, I write on loose leaf paper, I write in notebooks, I write in Markdown files.

I know that there’ll be plenty in there that can be put to good use, but which pieces are the valuable ones? Is it the fictionalised autobiography, written in the style of a Victorian novel? The submitted-and-rejected science fiction short about the future of the United Nations? The typewritten screed about the difficulties of iOS provisioning? The Platonic dialogue on the ethics of writing software?

One thing that’s evident is that a reorganisation is required. Blogs proceed temporally, but books can take on any other order. The disparate essays from my collection are related: indeed given the same emotional state, any given subject trigger leads me to the same collection of thoughts. I could probably recreate any of the articles in SICPers not from memory, but from the same initial conditions. There’s a consistent, though evidently evolving, worldview expressed in my recent writing. Connecting the various parts conceptually will be useful for both of us.

[By the way, there will eventually be a third part representing the descent: that part has in a very real sense not yet been written.]

Intra-curricular activities

I’m apparently fascinated by the idea of defining curricula for learning programming. I’ve written about how we need to be careful what we try to pay forward from the way we learned in the past, and I’ve talked about how we do need to pay it forward so that the second hundred years see faster progress than the first hundred years.

I’m a fan (with reservations, as seen below) of the book series as a form of curriculum. Take something like Kent Beck’s signature series, which covers a decent subset of both technical and social approaches in software development in breadth and in depth. You could probably imagine developers who would benefit from reading some or all of the books in the series. In fact, you may be one.

Coping with people approaching the curriculum from different skill levels and areas of experience is hard. Not just for the book series, it’s hard in general. Universities take the simplifying approach of assuming that everybody wants to learn the same stuff, and teaching that stuff. And to some extent that’s easy for them, because the backgrounds of prospective students is relatively uniform. Even so, my University course organised incoming students into two groups; those who had studied complex numbers at A-level and those who had not. The difference was simply that the group who had not were given a couple of lectures on complex numbers, then it was assumed that they also knew the topic from the fourth week.

Now consider selling a programming book to the public. Part of the proposal process with all of the publishers I’ve worked with has been describing the target audience. Is this a book for people who have never programmed before? For people who have programmed a little, but never used this particular tool or technique? People who have programmed a lot but never used this tool? Is this thing similar to what they have used before, or very different? For people who are somewhat familiar with the tool? For experts (and how is that defined)? Is it for readers comfortable with maths? For readers with no maths background?

Every “no” in answer to one of those questions is an opportunity to improve the experience for a subset of the potential audience by tailoring it to that subset. It’s also an opportunity to exclude a subset of the audience by making the content less relevant to them.

[I’ll digress here to explain how I worked that out for my books: whether it’s selfishness or a failure of empathy, I wrote books that I wanted to read but that didn’t exist. Therefore the expected experience is something similar to mine, back when I filled in the proposal form.]

Clearly no single publication will cover the whole phase space of potential readers and be any good. The interesting question is how much it’s worth covering with multiple publications; whether the idea of series-as-curriculum pulls in the general direction as much as scope-limiting each book pulls in the specific. Should the curriculum take readers on a straight line from novice to master? Should it “fan in” from multiple introductions? Should it “fan out” in multiple directions of interest and enquiry? Would a non-linear curriculum be inclusive or offputtingly confusing? Should the questions really be answered by substituting the different question “how many people would buy that”?

Preparing for Computing’s Big One-Oh-Oh

However you slice the pie, we’re between two and three decades away from the centenary celebration for applied computing (which is of course significantly after theoretical or hypothetical advances made by the likes of Lovelace, Turing and others). You might count the anniversary of Colossus in 2043, the ENIAC in 2046, or maybe something earlier (and arguably not actually applied) like the Z3 or ABC (both 2041). Whichever one you pick, it’s not far off.

That means that the time to start organising the handover from the first century’s programmers to the second is now, or perhaps a little earlier. You can see the period from the 1940s to around 1980 as a time of discovery, when people invented new ways of building and applying computers because they could, and because there were no old ways yet. The next three and a half decades—a period longer than my life—has been a period of rediscovery, in which a small number of practices have become entrenched and people occasionally find existing, but forgotten, tools and techniques to add to their arsenal, and incrementally advance the entrenched ones.

My suggestion is that the next few decades be a period of uncovery, in which we purposefully seek out those things that have been tried, and tell the stories of how they are:

  • successful because they work;
  • successful because they are well-marketed;
  • successful because they were already deployed before the problems were understood;
  • abandoned because they don’t work;
  • abandoned because they are hard;
  • abandoned because they are misunderstood;
  • abandoned because something else failed while we were trying them.

I imagine a multi-volume book✽, one that is to the art of computer programming as The Art Of Computer Programming is to the mechanics of executing algorithms on a machine. Such a book✽ would be mostly a guide, partly a history, with some, all or more of the following properties:

  • not tied to any platform, technology or other fleeting artefact, though with examples where appropriate (perhaps in a platform invented for the purpose, as MIX, Smalltalk, BBC BASIC and Oberon all were)
  • informed both by academic inquiry and practical experience
  • more accessible than the Software Engineering Body of Knowledge
  • as accepting of multiple dissenting views as Ward’s Wiki
  • at least as honest about our failures as The Mythical Man-Month
  • at least as proud of our successes as The Clean Coder
  • more popular than The Celestial Homecare Omnibus

As TAOCP is a survey of algorithms, so this book✽ would be a survey of techniques, practices and modes of thought. As this century’s programmer can go to TAOCP to compare algorithms and data structures for solving small-scale problems then use selected algorithms and data structures in their own work, so next century’s applier of computing could go to this book✽ to compare techniques and ways of reasoning about problems in computing then use selected techniques and reasons in their own work. Few people would read such a thing from cover to cover. But many would have it to hand, and would be able to get on with the work of invention without having to rewrite all of Doug Engelbart’s work before they could get to the new stuff.

It's dangerous to go alone! Take this.

✽: don’t get hung up on the idea that a book is a collection of quires of some pigmented flat organic matter bound into a codex, though.