Mathias Brandewinder on .NET, F#, VSTO and Excel development, and quantitative analysis / machine learning.
by Mathias 4. December 2011 15:47

I am in the middle of “Working Effectively with Legacy Code”, and found it every bit as great as it was said to be. In the book, Feathers introduces the concept of Seams and Enabling Points:

a Seam is a place where you can alter behavior in your program without editing it in that place

every seam has an enabling point, a place where you can make the decision to use one behavior or another.

The idea - as I understand it - is that an enabling point is a hook for testability, a place where you can replace the behavior of a piece of code with your own controlled behavior, and validate that the results are as expected.

The reason I am bringing this up is that I have been writing lots of F# lately, and it made me realize that a functional style provides lots of enabling points, and can be much easier to test than object-oriented code.

Here is a simplified, but representative, example of the problem I was looking at: I needed to pick a random item in a list. In C#, a method along these lines would do the job:

public T PickFrom(IList<T> list)
   var random = new Random();
   return list[random.Next(list.Count())];

However, this code is utterly untestable; it’s also probably a terrible idea to instantiate a new Random every time this is called, so we modify it this way:

public T PickFrom(IList<T> list, Random random)
   return list[random.Next(list.Count())];

This is much better: now we have a decent Enabling Point, because the list of arguments of the method contains everything that is used inside the method. However, this is still untestable, but for a different reason: by definition, Random.Next() will return different values every time PickFrom is called, and expecting a repeatable result from PickFrom is a bit of a desperate enterprise.


by Mathias 27. October 2010 15:14

When it comes to design discussions, I have been described as “opinionated” (at times, harsher words like pig-headed or argumentative – or way worse - have been substituted). It isn’t that I think I am usually right, and  I am normally a pretty gentle person, but I firmly believe in Socratic method for identifying well-formulated, clear and transparent solutions.

Two ingredients are required to make it work: an unambiguous statement, and a contradictor, who will poke at the statement until it either crumbles, or gets refined until it is self-evident, with clearly identified qualities and limitations. So I like to take somewhat extreme positions in design discussions, either in my proposals, or in my criticism. It has nothing to do with how much I believe them to be right, and everything to do with understanding what is at stake in the discussion and where the tensions are.

Unfortunately, it has also gotten me into trouble at times, because, well, discussions can get heated. I will honestly try my best to find issues with any design I am presented with, and push for clarification – just like I really appreciate when people do the same with mine. It’s a tricky exercise, because while these are ideas that are under fire, it’s often difficult not to take the criticism personally. I hope to get better one day at sensing when that emotional line is being crossed, so that an honest and open discussion can be maintained.

Anyways, the reason for this rant is that I am finally reading The Structure of Scientific Revolutions, by Thomas S. Kuhn - and I am enjoying it tremendously. The book is mostly concerned with science, but some of the ideas resonate deeply with me, and in my opinion extend beyond science. The two following gems are lifted from the book:

Truth emerges more readily from error than from confusion.

Sir Francis Bacon, quoted in Kuhn

… Novelty ordinarily emerges only for the man who, knowing with precision what he should expect, is able to recognize that something has gone wrong. Anomaly appears only against the background provided by the paradigm. The more precise and far-reaching that paradigm is, the more sensitive an indicator it provides of anomaly […] By ensuring that the paradigm will not be too easily surrendered, resistance guarantees that scientists will not be lightly distracted…

Thomas S. Kuhn

I could not agree more.

by Mathias 26. September 2010 08:12

The most awesome free developer event on the west coast is back again, and it looks like it will be even more awesome this year. The 5th edition of Silicon Valley Code Camp is taking place Saturday and Sunday Oct 9th and 10th, 2010, at Foothill College, in Los Altos Hill. There are 194 sessions, already over 1,600 registrations, with topics for all tastes - .NET, Java, Cloud Computing, Python, Javascript, mobile development, and more.

The 2010 schedule is up here. I will be giving 2 talks, on Test-Driven Development, and on Mocking. Both are on Sunday – hope to see you there!

by Mathias 20. May 2010 06:43

dotlesscss I gave a quick Firestarter talk at the San Francisco .Net user group yesterday about .less. .less (‘dot-less’) is an open source .Net library, which extends the functionality of CSS (it works with your existing CSS files), adding features like variables, using a syntax close to CSS. If you find that working with CSS causes some teeth-grinding , you should probably have a look!

Download the slide deck here

by Mathias 1. December 2009 11:33

I have been using test-driven development since I read Kent Beck’s book on the topic. I loved the book, I tried it, and adopted it, simply because it makes my life easier. It helps me think through what I am trying to achieve, and I like the safety net of having a test suite which tells me exactly what I have broken. It also fits well with the type of code I write, which is usually math-oriented, with nice, tight domain objects.

So when I decided recently to write a C# implementation of the Simplex algorithm, a classic method to resolve linear programming optimization problems, I expected a walk in the park.

(Side note:I am aware that re-implementing the Simplex is pointless, I am doing this as an exercise/experiment)

Turns out, I was mistaken. I have been struggling with this project pretty much from the beginning, and unit testing hasn’t really helped so far. Unfortunately, I didn’t reach a point where I fully understand what it is that is not flowing, but I decided I would share some of the problems I encountered. Maybe brighter minds than me can help me see what I am doing wrong!More...


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