16 August 2016

Absolute Priority Premise, an Example

Optimus Prime, Transformers ToysTransformation Priority Premise
I would like to start this article with Uncle Bob Martin's Transformation Priority Premise - TPP for short - which he defined in 2011. With the premise Uncle Bob gave an algorithm how to find the next test when doing Test Driven Development. During (classic) TDD we use transformations to change the code to get from red to green. For example when starting with a new method the very first test is usually red because the empty or generated method returns null. We fake the first test by changing that null to return a constant value, e.g. return 5. This transformation is called nil->constant and has a high priority. A later test might force us to add a conditional to enable another fake. This transformation is called unconditional->if and has a medium priority. Replacing the value of a variable, i.e. variable->assignment has a low priority.

According to Uncle Bob, these transformations have a preferred ordering. We should prefer higher priority transformations to pass tests and chose tests in a way that they can be passed with higher priority transformations. When an implementation seems to require a low priority transformation, we could backtrack to see if there is another test to pass first which does not need that transformation. The theme behind the TPP is that as the tests get more specific, the code gets more generic. If you want to know more about TPP, see Uncle Bob's cartoon follow-up on the TPP and Sorting and his talk on the Transformation Priority Premise.

Absolute Priority Premise
In 2012 Micah Martin set out to define some heuristics to compare code objectively and proof that some code is better than some other code. Building on the TPP's priorities he defined the Absolute Priority Premise - APP for short. The APP knows six components, i.e. basic building blocks of code, and assigns them a mass. The building blocks and their weights were
  • constant, a value in code has mass of 1.
  • binding, a name or variable has a mass of 1, too.
  • invocation, calling a method or function - mass 2.
  • conditional, any form of if, switch or case - mass 4.
  • loop, for or while loops - mass 5.
  • assignment, replacing the value of a variable - mass 6.
More complex building blocks have a higher mass. The total mass of a piece of code is the sum of the mass of its respective components. A lower value is better. The best set of specific values of mass are unknown and I will use Micah's weights. If you chose to count different, please let us discuss!

A detailed explanation of the Absolute Priority Premise is given in the two presentations of 8th Light University (8LU) - Part One and Part Two. See also Micah's Coin Changer Kata as a complete example of applying the premise.

Measuring the Mass of Code
I like Micah's idea to measure the mass of code. It might not be a direct indication of readability but simpler code is always better. I wrote six different versions of the Word Wrap kata and was wondering which one would be considered the "best". I should have calculated the mass of these algorithms manually, but I followed Terence Parr's advice, to avoid working by hand five days what I can spend five years of my life automating. I had to create a tool to calculate the mass of Java code - which of course took me much longer, especially as I verified the mass of each algorithm manually to make sure my code worked as expected.

Absolute Priority Counter
I created abpricou, the ABsolute PRIority COUnter. It parses Java source and collects its mass as defined by the Absolute Priority Premise. It is written in Python, because it was Python month when I started working on it. It uses the Python Java Parser plyj. plyj offers a Visitor API for parser events,
class CountingVisitor(m.Visitor):
    def __init__(self):
        super(CountingVisitor, self).__init__()
Constants and bindings are staight forward, e.g.
    def visit_Literal(self, literal):
        return self._a_constant_value()

    def visit_FormalParameter(self, parameter):
        return self._a_name()
Literals in the code are counted as constants and parameters are only names for values, thus bindings. A method or function counts as a constant for the code it represents and a binding for its name.
    def visit_MethodDeclaration(self, declaration):
        return self._code_is_a_constant()
Invocations, conditionals and loops are the same. For example
    def visit_MethodInvocation(self, invocation):
        return self._an_invocation()

    def visit_IfThenElse(self, conditional):
        return self._a_conditional()

    def visit_While(self, loop):
        return self._a_loop()
The only interesting case is the assignment. Not every assignment in Java is counted as an assignment, only re-assignments which modify values are counted. final fields or local variables are just names for expressions similar to parameters.
    def visit_Assignment(self, assignment):
        if ... :
            # code to ignore
            # final field is assigned in constructor
            # final local is assigned in block
            return self._an_assignment()
View the complete source of the Absolute Priority Counter on Bitbucket.

Let's see some code: Word Wrap Kata
As I said before, I developed the counter to calculate the mass of my different implementations of Word Wrap. I was interested in the mass of the algorithm and skipped constructs like class definitions. (I suppose a class definition is a constant for the code and a binding for the name.) I also ignored Annotations, Enumerations and Generics. The first algorithm uses recursion to loop over the blanks to find the end of each line. Its code is
   final char BLANK = ' ';
   final char NEWLINE = '\n';

   String wrapRecursive(String line, int maxLineLen) {
      if (line.length() <= maxLineLen) {
         return line;

      int indexOfBlank = line.lastIndexOf(BLANK, maxLineLen);
      int split;
      int offset;
      if (indexOfBlank > -1) {
         split = indexOfBlank;
         offset = 1;
      } else {
         split = maxLineLen;
         offset = 0;
      return line.substring(0, split) + NEWLINE
           + wrap(line.substring(split + offset), maxLineLen);
including the components
| Component   | Mass  | Count |
| constant    |   1   |   7   |
| binding     |   1   |   8   |
| invocation  |   3   |  10   |
| conditional |   4   |   2   |
| loop        |   5   |   0   |
| assignment  |   6   |   0   |
resulting in a total mass of 53. Further implementations have the following masses:Scales
  • The tail recursive solution has neither loops nor assignments similar to the recursive one and has a total mass of 71. (The source of this and all further variants is given in Word Wrap Kata Variants.)
  • The looping variant contains a loop and an assignment resulting in a mass of 68.
  • The optimised loop which avoids temporary String objects, contains a loop and an assignment and some more invocations. Its mass is 80.
  • The loop using a buffer saves even more heap allocations and needs more invocations summing up to 105.
  • The solution using Regular Expressions as shown in the original article has a mass of 55. Merging the parts of the expression into a single expression would save five invocations, but makes the expression less readable. I argue that the Regular Expression itself has some weight, as it contains one conditional ("|" in line 3) and two loops ("(.{1," + maxLineLen + "})" in lines 1 and 4). So a fair weight is 69.
  • The functional version using flatMap and reduce is quite verbose due the lack of inferred pair types in Java. As plyj does not support Java 8 I was unable to measure its mass.
First Conclusion on Algorithms
The most basic, recursive version of Word Wrap has the least weight. What does it mean? Is it the best version? It is the most compact version without playing Code golf, at least in Java. It does not mutate any variables but it puts the highest load on the Garbage Collector. All the discussed algorithms have different memory and run time performance characteristics. I had hoped for a clear answer what the best version would be and I am not seeing that. I challenge you to leave a comment with a version of Word Wrap with a smaller weight. Would it be considered better code?

The mass of the basic loop version seems too much compared to the recursive version. The current weights favour functional programming by putting a penalty on loops and assignments. Mutating a local variable has a smaller weight than mutating the state of an object. The looping version uses StringBuilder instead of plain String + which needs two more invocations for its construction. Then its components are
| Component        | Mass  | Count |
| constant         |   1   |   8   |
| binding          |   1   |  10   |
| local assignment |   1   |   3   | like a new local binding
| invocation       |   3   |  10   |
| conditional      |   4   |   1   |
| loop             |   5   |   1   |
| assignment       |   6   |   0   |
and its mass is 60 which is a bit more code than the recursive solution.

More Structure
The different wrap() functions above are just algorithms. They are not factored into parts that might change at different speeds over time and definitely violate the SRP. They also break the OCP as it is impossible to change the strategy of splitting without touching the logic of collecting. To address this I wrote another recursive version following Tell, don't ask,
interface Page {
   void renderLine(String lineOfProperLength);

class Wrapper {

   final char BLANK = ' ';

   final Page page;
   final int maxLineLen;

   Wrapper(Page page, int maxLineLen) {
      this.page = page;
      this.maxLineLen = maxLineLen;

   void wrap(String line) {
      if (line.length() <= maxLineLen) {

      int indexOfBlank = line.lastIndexOf(BLANK, maxLineLen);
      int split;
      int offset;
      if (indexOfBlank > -1) {
         split = indexOfBlank;
         offset = 1;
      } else {
         split = maxLineLen;
         offset = 0;

      page.renderLine(line.substring(0, split));
      wrap(line.substring(split + offset));
which is very similar to the tail recursive solution above, with a total weight of 56. The number is smaller because it does not contain the necessary implementation of Page.renderLine(). The shown code does less, which makes it difficult to compare. On the other hand Page.renderLine() might be used by other parts of the code as well, so it is not strictly a part of Word Wrap.

Moar Structure!1!!
Later I created an extremely factored and decomposed implementation of Word Wrap that separated concepts of rendering, splitting, accumulating lines and hyphenation rules which should fulfil both SRP and OCP. Ignoring the HyphenationRule because that is not covered by the other solutions, its mass is 167 due to many method invocations and parameter names:
| Component   | Mass  | Count |
| constant    |   1   |  17   |
| binding     |   1   |  33   |
| invocation  |   3   |  30   |
| conditional |   4   |   4   |
| loop        |   5   |   1   |
| assignment  |   6   |   1   |
There is a loop and an assignment, at its core this implementation is a looping one. Using the recursive solution I should be able to get rid of the loop and the assignment.

The Absolute Priority Premise counts the different components of a program and sums their weights. If the weights are correct than the program with the smallest mass would be considered the "best" program. This is not true for algorithms like the Word Wrap because the APP ignores features like memory usage or performance optimisation. For general purpose code the validity of the APP is unclear. It just measures the number of code constructs, favouring more compact, functional code. On the other hand the four rules of simple design encourage us to introduce explaining variables to reveal the intent of the code which is more important than fewer elements.

27 July 2016

Improving Typing Accuracy

Das Keyboard - Model S Ultimate (III)I am always interested to improve my typing performance and eager to use keyboard shortcuts. As Code Cop I mentor developers and pair with them in different environments. I need to improve my typing and shortcut-fu across different tools and use flashcards to memorise IDE shortcuts. I found that I need more visual hints to remember the positions of certain keys. I am able to touch type but I do not know the exact position of the keys consciously. This is sometimes a problem when typing passwords.

Using a Blank Keyboard
Iris Classon reported that using a blank keyboard improved her touch typing accuracy. She listed measurements and statistics on her web site regarding her improvements. I own a Das Keyboard Ultimate and have used it from time to time. It is true that using it improved my touch typing accuracy, but it did not help me to "know" where the keys were.

Key Flashcards
I want to memorise the exact locations of all keys on the keyboard. This is very difficult for me, but I want to master it. As with the IDE Shortcuts I used Anki to create a deck of flashcards containing all keys on the keyboard. It starts with pictures of the blank keyboard and the name of the key in question:
Where is the #'-key on a German keyboard?Showing the keyboard already on the front side of the flashcards - the question side - helps me visualise the location of the key. I use the TKL (tenkeyless) variant of the keyboard, ignoring the numeric keypad, to save horizontal space. When ready I advance the deck and see the key marked on the keyboard:Position of the #'-key on a German keyboardThe same layout on both sides of the flashcards help me keep my visual focus on the position. (Having two pictures for each card doubles the file size of the deck, which might be a problem on mobile devices running Anki but I had no issues when using the deck.) As I use German and UK layout depending on my pairing partner, I created two decks with German and UK layout respectively:I did not create these decks by hand, rather developed a sequence of little application that would allow me to mark the key positions on the image of the blank keyboard, render the keyboard with and without markings to be used in a deck of flashcards and write the CSV needed to import the deck into Anki. (See Keyboard Flashcard for more details and the source code.)

During my practise with the decks I sometimes wanted to separate letters from non letter keys. So I created even more decks:

18 July 2016

Hosting Public Coderetreats

I described the needs and benefits of inhouse Coderetreats in the previous article. (In case you did not read it - a Coderetreat is a full day hands-on coding workshop focused on the fundamentals of software development and software design. It is a day full of fun and excitement.) In this second part about Coderetreats I will say more about the opposite of (buying) an inhouse event, which is (hosting) a public one.

Hosting a public Coderetreat is obviously more work for the organiser, adding promotion of the event and handling registration. There are several reasons why companies host a Coderetreat. I ran a public Coderetreat in Venice sponsored by Interlogica. The people of Interlogica were passionate about our craft and wanted to connect with like minded individuals. Three out of four attendees were not connected with Interlogica at all and the exchange of ideas and networking was great.

Sponsoring a Coderetreat is Awesome!
The hosting company is usually also the Coderetreat's main sponsor. Sponsoring a public Coderetreat is a marketing activity. Interlogica wanted to increase its visibility. While we cannot expect a huge impact from a single event, it definitely was a good start. I supported them because a Coderetreat is real value provided to participants and the Craftsmanship community. As the event was free for the participants, someone had to pay for the room, lunch, time spent on organisation, my (facilitator) travel expenses and so on.

Session in progress at Coderetreat Venice 2016 (C) Pamela AdediwuraThe sponsor deserves our gratitude and at least some "link love". The host and facilitator may create more buzz on Twitter and other channels, depending on the free time the host has during the sessions. I post at least some images of the sessions and retrospectives, drawing some attention to the sponsor as well. As sponsored event, this is part of the deal.

Finding Local Talent
Many companies have trouble finding developers to hire. Hosting a public Coderetreat is a great way to present the company. Sometimes a representative of the sponsor will open the Coderetreat and make participants aware of open positions. I recommend distributing handouts of vacancies in the room and on the tables.

Public Coderetreats are run on Saturdays to allow people to participate. Starting Saturday morning attracts only the most passionate developers, who want to learn and engage in deliberate practice. These are exactly the kind of developers companies want to hire. A lady from Interlogica's marketing department told me that "people who understand (the idea of Coderetreat) and come are the people we want to hire."

Community and Networking
The Software Craftsmanship community is growing and a Coderetreat is also a networking event. After a few Coderetreats the participants get to know one another. For me a Coderetreat is like a class reunion, I usually know at least half of the participants and some of them are dear friends whom I would like to meet more often. For beginners or people new in the city it is a great way to get in touch with local craftsmen.

A Coderetreat ends with drinking beer in a local pub in the evening. This is another opportunity to talk to fellow software professionals. At the Coderetreat in Venice, the sponsor set up a small reception including cheese, wine and finger food for all participants. (Did I mention that they rock ;-) Interlogica's CEO was amazed by the number of different people he met and talked to during that time.

Free for Participants
According to Corey Haines, one early proponent of the Coderetreat format, the event must be free of charge for participants. Many organisers ask people only for a safety deposit of ten to 15 Euro. The deposit is refunded as soon as the person shows up and is used to pay beer in the evening if the person does not. I strongly recommend using such a safety deposit to make sure that people show up. Most organisers use Eventbrite for handling the registration, because it does not take any fee when a ticket is refunded. An Eventbrite registration page might look like the one I used for GDCR14.

Promoting the Event
After setting up Eventbrite, every public Coderetreat should be registered at coderetreat.org and promoted through Twitter, Facebook and other channels. Coderetreats in large cities, e.g. Berlin or London are sold out in under a week. In smaller communities we need to allow enough time for people to get spread the word that a Coderetreat is coming up. I recommend having the registration ready at least one month in advance to have enough time for sharing and advertising the event.

Whenever I run a Coderetreat, I talk directly to local programming language user group leaders and ask for their support to promote it. Even if I do not know these group leaders, their members might be interested in coding activities. As a Coderetreat is open to any programming language, it is much more fun to have participants from various programming backgrounds. Collaborating with user groups ensures that there are participants offering more interesting languages like Go, Elexir, Haskell, Dart and so on.

you are awesomeThe same is true for women in technology. For a Coderetreat in Berlin last year, one facilitators got in touch with several local women-only programming groups, like Rails Girls or PyLadies, told them about the event and opened private registration for them. He waited for a week before making the registration public. After public registration started, the event was sold out in a week.

Being Awesome!
So if your company wants to be seen to care for craftsmanship, dedication and quality, you are looking for great developers to hire or you just want to work in an awesome company, hosting a Coderetreat is the right things to do. Even when you are not able to host a full Coderetreat, buying food for participants or covering expenses is appreciated.