Friday, August 2, 2013

The Great Software Lie

/* Temporary Fix 
 * 
 * No time write a proper blog entry, I'll get back to it later
 * Dave T 
 * 2nd Aug 2013
 */

Monday, June 3, 2013

The Splinterface

It starts off well, you have a class which has grown too complex, so you pull out some functionality into a separate class. You've pulled it out because now it is no longer fixed. It can be cyclic or non-cyclic perhaps.

All is good.

There are some parts that are shared by cyclic and non-cyclic, so you pull them out and create an interface. But over time, cyclic and non-cyclic diverge. You add a method to the interface that's only used by cyclic, and another which is specific to non-cyclic.

And eventually you can add comments to your interface that look like this

// cyclic uses these
...
// non-cyclic uses these
...
/// this one is shared by both
...

Now you have a Splinterface.

It provides the illusion of shared functionality and shared code, but that's all. It hinders change as you have lost clarity of what is and is not used. It promotes code duplication.

It's cause seems to be allied to designing interfaces based on what something is, not what services it provides.

Chances are you have 2 implementations of your Splinterface and liskov substitution is gone out the window.

Really it's time to stop, document what's going on in your code, take a long hard look, understand what should be done and fix it.

Or you could just add more code and hope for the best. If you take that approach, let me know how it all works out.

Ps- Thanks to JackH who came up with the name.


Monday, May 6, 2013

How long will that take?

OK, that's a got scope for a book. A long book.

But I remember a long time ago I did a small fixed price contract for a company. They wanted me to add some "simple" functionality to an existing app. They had the source, but no-one to do the work.

I'd never done a fixed price contract before, but I knew I'd never got any estimates right. I didn't like the idea of a fixed price contract much.

I started with - If you want a fixed price, pay me for one day to do the spec & estimates. This was (very) grudgingly accepted.

I sat down and broke down what needed to be done. With each part, I continued to break it down to the level where I knew exactly what was needed, and I knew that part would take less than 1/2 a day.

Anything longer than a Day was broken down more.

I went back with the estimate. I think it was about 3 weeks work. It's a long time ago. The manager thought I was winding him up, he'd expected about 3 days, not 3 weeks.

I had brought my list.

We went though the list piece by piece, and about 1/3 of the way through he said "Fine".

It took 12 days, not 15.

This was a task which had no unknowns for me. Each individual part was something I'd done already somewhere else, or at some other time.

Consider the amount of work that would be required to estimate a 3 month project for 6 people, working with 3 new pieces of technology that no-one on the team has used before. If you have not done something before, with a particular tool, it is possible that there's a snag. Do a simple test. Can I serialise the data as XML? Opps, the files are HOOOGE. We have to use something else.

Everyone wants accurate estimates, but no-one wants to put in the leg work to come up with the estimates.

You can of course still be wrong, but hopefully, not off by a factor of 5.

Friday, March 15, 2013

Church and State

It's been a while. Which means I've probably been having too much fun doing other stuff.

We recently saw the election of a new Pope, and I was thinking about some countries which embed their religion into the law of the land. The USA makes a big deal about separation of church and state, and I think that's a good thing.

 In software we often make a token effort to separate things. How many people remember their first program in college looking something like


            StreamReader streamReader = new StreamReader(_fileName);
            while (streamReader.Peek() >= 0) {
                string line = streamReader.ReadLine();
                if (line != null){
                    IEnumerable data = parseLine(line);
                    double sum = 0;
                    foreach (double d in data){
                        sum += d;
                    }
                    Console.WriteLine(sum);
                }
            }

So right from the start, we teach kids to bind Where we get the data, What we do with it, and Where we send the results.

Separation of functionality?

  • We could get the data and pass in an iterator
  • We could wrap the stream in a class which implements an IEnumerable
  • We could write a separate class parse Class, and pass it in.
  • We could write a separate sum() action and pass that in.
  • We could return the result as an iterator, which would execute as we step through.
We could end up with 4 separate, useful small classes which could be reused and mixed to suit our needs.

We could even hand off the Loop to Linq.
Imagine the resulting code

            enumerableFile = new EnumerableFile("sample.txt");

            var results = enumerableFile.Select(
                    s => ParseStringToDoubleList.parseLine(s).Sum()
                );

Now I can write unit tests for ParseStringToDoubleList() - Ok, an appalling name, but that's an others days work.

I can use Linq's Sum function.

If I want averages instead, no problem. 

I now have a tool-kit to build functionality

First we learn to build programs, then we learn to build tools to make better programs. 




Thursday, July 26, 2012

Ceci n'est pas une interface


Likewise, extracting all the public functions from a class and surrounding them with

public interface ISomeClassName { 
 
}

Does not make an interface.

One of the terrible failings of Resharper is the Extract Interface dialog has a button for All Public functions.
This encourages this frankly misguided behaviour.


IEnumerable is an interface. It defines one thing and it defines it will. Wander into any code base and if you have a decent environment, you should be able to do some form of "Find Usages" which will show classes that implement IEnumerable. There will be quite a few. That's because it's REALLY useful.

If I take a Binary Tree, there may be many different functions, allowing me to add Ranges, delete Ranges, create Views, Find Items, Get Counts, etc etc. How do I benefit from extracting the entire public interface to create an IBinaryTree. It would likely turn out that the interface has so much in it that the only thing which can implement it is another Binary Tree.

Maybe I have a lump of code which wants a Binary Tree, but in fact it really only cares about a collection which has been sorted into a given order. SortedCollection (or if you must ISortedCollection) might be a perfectly reasonable interface.


When we look at the members that my code uses, it comes down to iterating through the list...


public interface ISortedCollection
   IEnumerator GetEnumerator();
}


So in fact my code just needs an IEnumerable. It does not need an IBinaryTree at all.*


If I pass in an IEumerable then I can actually use a List for my code after calling List.Sort().


Now we are down to what an interface is. An interface specifies some functionality that I want to use. Ideally the minimal functionality. It is so much less than a list of public functions in an existing class, and in being less, it is more.


Now my Unit Tests can be far simpler, I no longer need to have test which depend on the binary tree. I can use a simple Array which I define in sorted order. 


Small interfaces reduce unnecessary binding. 


* You could argue that a specific interface for Sorted data would allow me to catch, at compile time, the problem of passing unsorted data down here. This is true, but that's a whole other post.

Friday, July 6, 2012

Open/Closed Principle

With so many things interrelating, it's hard to explain the importance of one thing without relying on many other bits of knowledge.

Open/Closed is on of those things.

How can software be Open for Addition and Closed for Modification.

Surely I need to change code? And change it all the time.

Well, maybe.

If I write smaller functions, and smaller classes. If they do one thing, and do it correctly, then they probably don't need to change. Ever.

My larger blocks of functionality, which are made of the smaller blocks, will change more often, but if, for example I create a class or function to do a bilinear interpolation of a surface, then as long as it does a bilinear interpolation, I may need to optimize it, but it will only ever do a bilinear interpolation. If I want to do some other interpolation, I create a new class.

My higher level class may change to use the new interpolation, but I have not CHANGED the bilinear one.

I may wrap the General Bilinear interpolation in a class which is better named from the point of view of the problem domain, and takes domain named parameters. Rather than have an Bilinear.Interpolate(double x, double y)->double  my wrapper may be myChemicalMix.ApproximateReactionRate(double tempInCelcius, Acidity ph) -> ReactionRate.

Now my domain class does nothing but map my domain problem onto an interpolation. I no longer have to remember is x the Acidity or the Temperature.

So now when I change from a Bilinear Interpolation to a Triangular Interpolation, my Bilinear Class remains untouched, I write my Triangular Interpolation and Unit Tests, and if it turns out that they can each implement a Surface Interpolation interface, happy days.

Nothing in designing software stands on it's own. That's why it's easy to write a program, but it's hard to engineer one.

Without Single Responsibility and Dependency Inversion, Unit testing is staggeringly difficult.
Without The Open/Closed Principle, you will spend all your time changing tests.
Without Interface segregation, you won't understand what you need to mock out for a given test, and the test will be overly complex.

Good design can only come from understanding why.



* yes, I did make those up from thin air

Tuesday, June 5, 2012

What's a tractor for

Imagine that you teach someone how to drive a tractor, how to hook up a plough, and you send them out into the field.

At no point do you mention crops, seeds, harvesting, food, or seasons. You don't speak of fertiliser nor crop rotation.

When you come back the field is full of staggering, incredibly complex and mostly useless furrows.

In the same way we seem to teach people how to use polymorphism, lambda functions, inheritance, iterators, and other tools.

But somewhere along the way no one has pointed out the fact that what we are doing is trying to make it easier to write and maintain code. In addition, it would be nice if we could also make it easier to be sure the code is correct. 

It seems that we have taught the how, not the why.

In the good old days of C++ the general comment was that in your first program you learn how to overload the operators, in your second program, you learn not to.