The Second Edition of "Refactoring"
For the past two years, I've been working on a second edition of my book "Refactoring". Here I have details about the new edition and some memos describing my thoughts in the last months of this project.
The book is in production: we hope that it will be on the shelves early in the fall.
I was lucky enough to work with Kent Beck on the C3 project that birthed Extreme Programming. There was a great deal I learned (and am still learning) from Kent, but one thing that really stood out was they approach he took to continually reworking the code base to keep it healthy, an approach that went under the then-unknown name of "Refactoring". In my other consulting work I stressed how valuable a technique this is, but couldn't point people to a book to learn about it, so I ended up writing it myself. It was published just before the 20th Century ended.
That's nearly twenty years ago, and the technique is now more widely
known, although often not executed as well as it should be. The book has
also held up pretty well, and I think you can take this old book and still
learn how to refactor pretty much as well as you could all those years ago.
But the book shows its age, with wrinkles like the use of
So over the years I've been thinking about revising it, but I have also been reluctant. After all it still teaches the technique perfectly well, and second editions have a horrible habit of not improving on the original. But a further force has been tugging at me. At the time I wrote it, it was becoming mainstream to consider classes as the dominant structuring the mechanism for code. These days, however, we see other structures playing a greater role. Classes still are valuable, in my view, but our refactoring needs to be less centered around them, realizing that they can come and go as code is trained into new shapes.
During 2015 and early 2016 I wrote a series of essays exploring various circumstances for refactoring, this helped me get a feel for if I should tackle a rewrite, and if so, how. By mid 2016 I was ready to commence the work in anger. If you've been wondering why I haven't been writing as much for martinfowler.com as I used to, it was because my writing energy has been focused on the book since then.
Changes in the Second Edition
The changes are both very minor and all-encompassing. They are minor because the basic structure of the book hasn't changed. I begin with an opening example, a chapter of principles, a survey of "code smells", and an introduction to testing. The bulk of the book is a catalog of refactorings and of those 68 refactorings, all but 10 are still present, and I've added 17 new ones.
Despite this lack of change in the overall book structure, the changes to the words on pages is huge. Every chapter and refactoring has been rewritten, mostly from near scratch. I rarely had decent opportunities to cut and paste text from the old edition.
The reorientation towards a less class-centered view is a large part of this. Although that may sound as simple as changing the name of "Extract Method" to "Extract Function", it did entail rethinking all aspects of every refactoring. I needed to reconsider the motivation, often feeling that it needed to be reframed. The mechanics needed at least a detailed review, often a complete rewrite. I wasn't keeping detailed notes on this, but my feel is that for every relatively simple import of an old refactoring, there were two that required a complete rethink.
However there is another change, which in a way isn't that important, but is bound to get a lot of attention. The examples are no longer in Java.
When I choose a language for examples in my writing, I think primarily of the reader. I ask "what language will help the most readers understand the concepts in the book?" Refactoring isn't a language specific book, its advice may have been explained with the help of examples in Java, but the refactorings apply to most languages. I picked Java because I felt the most people would be able to understand the code examples if they were written in Java. That was the case in 1997, but how about in 2017?
A Web-First Book
The world-wide web has made an enourmous impact on our society, particularly affecting how we gather information. When I wrote the first edition, most of the knowledge about software development was transferred through print. Now I gather most of my information online. This has presented a challenge for authors like myself, is there still a role for books, and what should they look like?
I believe there still is role for books like this, but they need to change. The value of a book is a large body of knowledge, put together in a cohesive fashion. In writing this book I need to gather together lots of refactorings, and organize them in a consistent and integrated manner.
But that integrated whole is an abstract literary work that, while traditionally represented by a paper book, need not be in the future. Most of the book industry still sees the paper book as the primary representation, and while we've enthusiastically adopted ebooks, these are just electronic representations of an original work based on the notion of a paper book.
With this book, I'm exploring a different approach. I think of the canonical form of this book as the web site. The paper book is a selection of material from the web site, arranged in a manner that makes sense for print. It doesn't attempt to include all the refactorings in the canonical book, particularly since I may well add more refactorings to the canonical web book in the future.
Our intention is that when you buy a copy of Refactoring, 2nd Ed, you might buy it at a bookstore in its physical form, or online in any form. The most essential thing you get for your money is the access code that gives you permanent access to the web site. You can read the physical book, and access the web site whenever you need.
This raises a question of what role ebooks (such as epubs and kindle books) should play. There is a strong argument that they should contain all the information on the web site, after all physical size isn't a factor, and ebooks can be updated easily if I add new material. However the book industry doesn't think that way, they expect ebooks to have the same content as the physical books, so the ebook versions of refactoring will follow that principle, at least for now.
Earlier Memos ▶
Keeping the scope the same (28 March 2018) ▶
One of the things I want to stress about this edition, is that it doesn’t cover more scope than the existing book. There is somewhat of a shift away from a purely class-based structure but my aim has been not to change the scope of the book too much. While there’s a lot of appealing territory I could explore, I have a limited amount of time and energy. So I followed a rule of not letting the second edition venture into new topic areas. Even with just trying to do no more than replicate what’s in the first edition, it’s still two years of solid work. I didn’t want to increase the amount of time I’m spending on this, after all the first edition is very successful, so my aim is to maintain its usefulness, not to try and create something new.
There’s a good chance that in the future, I will explore some new topics, and add to the corpus of refactorings on the web site. Of course, I thought that before with the first edition, but mostly didn’t, so take that thought with an appropriate amount of salt. But I did explore some essays on using refactoring to help explore various architectural problems in 2015 and early 2016. I enjoyed writing them, and they indicated a vehicle I could easily use more in the future.
Working through review comments (03 April 2018) ▶
I’ve spent the last few days (yes, including the weekend) working through review comments on the book. Early in February my editor at Pearson sent out the current state of the book to various people for a technical review. This is a vital part of the process for writing a book, any author will make mistakes, and I make plenty. Reviewers help catch those, and also highlight things that are not clearly explained.
This isn’t the first review for this book material. When I started the book I gathered together a panel of people to do on-going review. Every time I finished a chapter, or a couple of refactorings, I’d send it to them for comments. Their feedback has helped enormously. But at some point I need someone to step back and take a fresh look at the whole book, which is where these recent reviewers have come in. Currently I’m going through comments from four such reviewers: William Chargin, Michael Hunger, Bob Martin, and Bill Wake (who was also part of my on-going review group).
I like to do this on a chapter by chapter basis, take the first chapter, look at everyone’s comments, and process them all on the chapter. “Processing” means reading each comment, and deciding what to do about it. Each comment is a perspective from the reviewer, some might indicate a suggested change, perhaps an expression that something isn’t clear, perhaps an error in the code. Often I don’t do anything in reaction to the comment, I might disagree with someone’s suggestion, perhaps because I feel it’s out of scope for the book. Michael (who has reviewed previous books for me) feeds me lots of good suggestions for additional material that would take years to follow up on, so I have to let most of those go by. But I don’t mind because sometimes those suggestions are things that really need to be there, and I’m glad I had someone prod me to include them.
Errors are the obvious things to fix, and I’m regularly astonished when reviewers find subtle code errors. I avoid many of those by my automated code import system, but there are holes in the auto-import, and they’ve already saved me some embarrassing mistakes. Michael is particularly good at this, he must have installed several compilers into his wetware, which is one reason why I find him such a good reviewer. William Chargin is challenging him however, so I feel doubly blessed.
Clarifications are often the hardest to figure out. Sometimes a reviewer just says “I don’t understand this”, sometimes it’s more indirect - they suggest something that implies they didn’t understand what I was saying. Dealing with these is hard because I then have to judge whether it’s just a one-off thing, or something deeper. People will always have difficulties with bits of a book, trying to fix every individual difficulty would be cure worse than the disease - the book would have to be much bigger, and the prose would get so stilted that it would be tedious to read. It helps when more than one reviewer has the same difficulty, then I can be confident it’s something I need to fix. An example of this was the way I laid out nested functions in the opening example confused three of the panel, so I knew I had to try a different approach.
I always rather enjoy working through review comments. It’s good to get some feedback on whether what I’m doing is making sense. This stage is particularly good as it forces me to step back too. For nearly two years I’ve been down in the details, cranking chapter by chapter. Now I can look at the material as a whole, yet still dive down to sort out important details.
Refactoring takes the Red and Black (05 April 2018) ▶
When I wrote the first edition of Refactoring, it went into the Object Technology Series at Addison Wesley. I never took book series very seriously, so I just followed my editor’s suggestion. Since then I’ve formed my own series (the “signature series”), and put a fair amount of effort into curating it so it only contains books I can firmly recommend. So it’s natural for the book to move into my own series.
It isn’t, however, an inevitable decision. The series isn’t a catch all, it’s about books that I consider to be foundation books on the technical side of programming. I submitted my most recent book, NoSQL Distilled, for the series, but I rejected it - because I didn’t think it fit in with the flavor of the series. That sounds rather convoluted, but there is a process here. Every candidate book submitted to the series is sent to all the authors in the series, and I ask for their opinion. In that case, they helped me decide to reject myself. This time they felt it was an easy inclusion, which reinforced my feeling that it was a good fit.
Pause in Review Updates (06 April 2018) ▶
As I said in an earlier memo, I’m enjoying going through review comments. However I’m about to put this work on a long pause. I have travel commitments coming up that means that today is the last day I’ll get at my desk for five weeks. While I can technically do some writing work while I’m on the road, I’ll mostly be too busy with other things to put any serious energy into it. (And there is some vacation in there, which I hope will help rejuvenate me a bit.) It’s a frustrating break, since I’d really like to get the text of the book settled so to better concentrate on other things. I’d hoped to have all the review comments processed and dealt with by now, but plans in writing are little better than plans in software development (for much the same reasons).
Back at my desk (18 May 2018) ▶
This week was the week I finally got back to my desk in New England after five weeks on the road. It was a long time away, but I can’t complain too much since the last couple of weeks were an excellent vacation in Croatia. Highlights were Split, Dubrovnik, the Paklenica national park, and especially the Plitvice Lakes.
I had hoped to have finished the text before I went away, but there were still some review comments that needed work. I also got a final batch of comments just before I left. So this week I made my first pass through that final batch and now just have the outstanding todos from the reviews. The bad news is that all these todos take a bit of effort to fix, since they became todos since I couldn’t quickly fix them while going through the comments. The good news is that I only have fourteen of them. I will hopefully get through them over the next two weeks before I have to hit the road again.
Another topic on the book this week was starting to think about the cover. The core cover design is already settled, as it will be part of my signature series, but it does mean I have to pick a photo of a bridge. We’re in the middle of sorting that out now, hopefully I’ll be able to share that next week.
Reworking examples (25 May 2018) ▶
As with last week, this week has seen me working on review comments so I can finalize the technical content of the book before starting the production process. I went through all the comments last week, doing all the easy ones that I could deal with in less than an hour or so. That left the complicated ones, which are pretty stressful to be working on at this late stage in the game, with a (admittedly, somewhat self-imposed) deadline staring at me.
At the heart of my work this week is reworking two examples. Both were ones where a couple of reviewers found difficult to follow, so I needed to figure out something that I think will be easier. This isn’t just about changing the prose text, it’s also about reworking the code. I find code examples to be one of the most difficult aspects of my writing. I try to create examples that are just complicated enough to show the main point, but no more complicated that that. They are still artificially simplistic - any realistic example is just too much for most readers to get their head around - but I want them to resonate with readers’ day-to-day experience. Today I spent most of the day coming up with an example that’s about fifty lines of code. I think it captures what I’m trying to say, but I’ll learn more as I carry out the refactoring I’m illustrating on this code and see how my prose works with it. I’m optimistic that it will work, but there’s still a fair bit of uncertainty.
The earlier example was particularly tricky as it was a section of a larger refactoring example, the future opening example of the book. This example divides into three phases, and reviewers indicated problems with the middle phase. I reworked the sequence of the refactorings, and hopefully things are much clearer now. Interestingly this refactoring centers around a refactoring (Split Phase) that I hadn’t written up before my first draft of the opening example. The essence of the change was to follow the now-written mechanics of this new refactoring, and I was happy to see that following these mechanics seemed to make it a good bit easier to do and understand. The mechanics sections in my book aren’t the only mechanics for a refactoring, and they can’t be the best for all contexts. My aim is that they should work pretty well, most of the time. So I was pleased that following them helped me through this example.
Reworking refactoring examples like this make me very familiar with git. I like to keep all my code examples “live”, so that I can change the code, run tests to ensure it still works, and mark sections of it to automatically flow into the book text. I’ve done this for many years with code examples, and it’s made life much easier. But doing this is tricky with refactoring, since I have a sequence of changes to the code. To cope with this I store the refactoring sequence in a git repository (necessarily a separate repo to the one that stores the book’s text) and capture the refactoring as a sequence of commits. I then import the code into the book text with tags that indicate the ref of the commit, and the name of the code fragment. When reworking a sequence of refactorings like this, I do a lot of cherry picking, where I make a change to commit master~7, then cherry pick all the refactoring changes I did since onto the changed commit. It’s awesome when it works well, and even when it doesn’t it’s far better than what I had to do with the first edition of the book.
I have one more week at my desk before I’d like to declare “done”. The target still seems plausible, although much will depend on how the fifty lines I wrote today works as I write about the refactoring steps that go with it.
Released to Production (01 June 2018) ▶
As May ended, I hit an important milestone, referred to by my publisher as “release to production”. In the days of traditional publishing, this means that the author hands her manuscript over to the production team. At this point we expect no significant changes to the core material of the book. There will be changes: as the book goes into copy-edit, as well as things like indexing - but they won’t be material changes to the essence of the book.
In my early books, I’d send electronic files over to Pearson, and at some later point I’d get a big print out of changes marked up by the copy-editor. Other than going through these changes, checking to see if I agreed with them or not, I’d have little more to do with the book before it appeared on the shelves. These days, the process is rather more interactive, the copy-editor and I will share a git repository and I’ll be looking at diffs to see his suggested changes. But the sense of crossing an important bridge is still there. I won’t be reworking any more examples, or adding any significant material. At some level, the book is done. (Although, since this is a web-first book, I intend to continue to evolve its web representation).
I have a sense of relief, although there is still much to be done with the book, this is still a big milestone, a sign that my focus on the book will begin to wane. I don’t have too much relief, because I have to go to Madrid next week for a couple of talks, and speaking trips are less appealing to me than a trip to the dentist. But it is some weight taken from my mind.
Latest Memo: The new cover
13 June 2018
When we started doing the signature series, the cover designer laid out the basic design which included space for a different photograph with each book. I decided that these photographs should follow a theme for all the books in the series. At that time my wife, a structural engineer, was designing bridges; she has since moved from horizontals (bridges and tunnels) to verticals (buildings). Her involvement in bridges inspired me to use them as a common theme for the book. So whenever an author writes a book in my signature series, I ask them to choose a bridge to adorn the cover. Ideally the bridge should have some personal connection for them.
For my first book in the series (Patterns of Enterprise Application Architecture), I picked the Zakim bridge in Boston. The link was pretty clear - they built the bridge just down the road, during the same years that I wrote the book. For my second series book (Domain-Specific Languages), I picked the Iron Bridge - this was a connection to the Black Country where I grew up, as well as a historically important bridge.
So what to choose for the Refactoring book? One thought that occurred to me was if I could draw some kind of analogy between refactoring and bridge engineering - but discussion with the bridge engineers I know made it clear that there’s nothing in bridge engineering that is comparable to refactoring. So instead my mind turned to a non-professional association. In this case I started thinking about one of my favorite places that I’d visited many times in the two-plus decades I’ve lived in New England - Acadia National Park. This immediately suggested picking one of the many attractive bridges that are on the carriage roads.
But I also thought of another Acadia-tinged possibility. On the road to Acadia we cross the Penobscot River. At the time that I wrote the first refactoring book, the road crossed the Penobscot using Waldo-Hancock Bridge, a suspension bridge designed by the notable bridge engineer David Steinman. In the first years of the new century, however, they found that the 70 year-old bridge needed to be replaced, and by 2007 the road went over the new Penobscot Narrows Bridge.
On one of our trips up to Acadia, we stopped so I could take some photos of the two bridges. I’m glad we finally did do that, because a year later the Waldo-Hancock was demolished. (It’s a shame that I took my photos on such an overcast day.)
Although there aren’t any analogies I can draw between bridge engineering and refactoring, I can push myself to summon up creative analogies between the two editions of the refactoring book and these two bridges.
Although various twitterers have commented that the second edition of the refactoring book “refactors” the first edition, that isn’t true. (Indeed, as with bridge engineering, I don’t think there is any analogy from refactoring to book writing.) This second edition is a replacement to the old one, in the same way that the Penobscot Narrows bridge replaces the Waldo-Hancock. The Waldo-Hancock demonstrated innovative techniques that reduced the cost of bridge building, in the same way that the refactoring book described a new technique that reduces the cost of building software systems. The first edition of the book is replaced by a new edition within my signature series, and the new Penobscot Narrows bridge is a similar design to the Zakim bridge that was the cover bridge for the first book in that signature series.