Algorithms

While looking for a job I went on an interview which was focused on my ability to come up with solutions to algorithmic problems, and fast. The interviewers were sure it is the essence of the job (job title read: Senior C# Developer). I have always believed, my job is to create architectures that last and -- among other things -- I do like patterns that make algorithms unimportant, interchangeable. From my experience, it's rarely even required to optimize algorithms, and I never do this until a performance impediment arises (which is also rarely the case).

What's your take on this? Must a good software developer be fast and efficient when creating algorithms -- or is it more like a nice-to-have-but-not-necessary thing? (The answer may depend on the specifics of your project.)

Latest Brainbench Test

I've scored 4,51 on a .Net Framework 3.5 Fundamentals Brainbench test today. The transcript is here.

It says: "Scored higher than 99% of all previous test takers."

(Boasting does not really suit me. It can very well be the case that I was the second guy to take the test in the whole world. And that other guy fainted after the 3-rd question because his heater had burned out all oxygen in his room!)

State and CycledEnumerator

The GoF State pattern is not on top of my list of favorites (Decorator is), but I am using it from time to time. And as you probably are aware there is this question about the implementation of State: whoever will switch between states and when?

I thought that Iterator -- another GoF pattern -- might be a good example of something that encapsulates state switching logic in some cases, when the states are switched strictly in the order you know beforehand. I realize that not every State implementation is that simple, but if yours is, you might want to use the idea: just pass the IEnumerable of IState to the implementation of State, and use MoveNext() and Current {get;} on the Enumerator internally to switch states. If you are doing something like this, it might be a good idea to jump back to State #1 after you've reached State #Last. I've written a little helper class to do just that:

using System;
using System.Collections.Generic;

namespace Primitives
{
    public class CycledEnumerator<T> : IEnumerator<T>
        where T : class
    {
        private LinkedList<T> _chainedObjects;
        private LinkedListNode<T> _currentObject;

        public CycledEnumerator(IEnumerable<T> objectsToChain)
        {
            if (objectsToChain == null)
            {
                throw new ArgumentNullException("objectsToChain");
            }

            _chainedObjects = new LinkedList<T>(objectsToChain);

            if (_chainedObjects.Contains(null))
            {
                throw new ArgumentException("Nulls are not allowed.", "objectsToChain");
            }

            if (_chainedObjects.Count < 1)
            {
                throw new ArgumentException("Need at least one item in the set.", "objectsToChain");
            }

            this.MoveBeforeFirstElement();
        }

        private void MoveBeforeFirstElement()
        {
            _currentObject = null; // I don't like nulls at all, but I'm putting it here for the sake of consistency with Microsoft's implementations of Enumerator (which is a variant of GoF Iterator pattern).
        }

        public T Current
        {
            get
            {
                return _currentObject.Value;
            }
        }

        public void Dispose()
        {
        }

        object System.Collections.IEnumerator.Current
        {
            get
            {
                return _currentObject;
            }
        }

        public bool MoveNext()
        {
            if ((_currentObject == null) || (_currentObject.Next == null))
            {
                MoveToFirstElement();
            }
            else
            {
                _currentObject = _currentObject.Next;
            }

            return true;
        }

        private void MoveToFirstElement()
        {
            _currentObject = _chainedObjects.First;
        }

        public void Reset()
        {
            this.MoveBeforeFirstElement();
        }
    }
}

(That said, I don't like Iterator much (and all of its buddies, like the Enumerator): it exposes too much of its state to the client, and has too complex a contract. It's all like "if MoveNext() returns true, then Current contains the next element", or: "after initialization the Enumerator is positioned before the first element, and you should call MoveNext() to get anything from it".)

Gang Of Four Patterns

Some days I find myself really believing that Gang Of Four patterns describe about 90% of all domain-model-related software design tasks out there. On our last design meeting I only had to name the applicable patterns, and that about did it: "Huh, this can be done with a Visitor", or "Sounds like an ordinary Composite to me"... That is not to say I'm good, but rather to reiterate what this guy told me once: "Everything has already been written".

("Design Patterns: Elements of Reusable Object-Oriented Software" was one of the first books I've read on the subject, years ago, and it's a really good read.)

Databases vs. everchanging model

This sprint I've been struggling hard to postpone the creation of a database to back up WCF service operations 'till next sprint. Last sprint I've insisted on keeping the store of service objects in memory - so the service loses all data upon restart. This was enough to make an iteration (and I think it was a good decision) but a lot of people on the team pushed back.

The reason I don't want a database from day 1 is our domain model is undergoing such changes that it would have taken us an entire sprint redesigning the database for every change, if we had decided to go down that road. We've spent that time on useful things instead, I hope.

Last week we, again, came to a point where a decision was needed on whether to create the database or not. And once again I pushed back, so we've chosen to save all data into a single file (having more than one would require extra work for reconstructing object references) using plain old data contracts. A question came up though: how do you save all those different collections of domain model elements preserving object references between those collections? The answer to that was dumping all objects into a List<object>, creating a DataContractSerializer around it (with exactly that type - List<object>), feeding to the serializer a list of known types made of all types of contracts (note that it's no longer domain model elements) that are used to store the state of the service, telling the serializer to preserve object references. Of course, all of this would still be hard to do (because of reference fixups), if we had not decided to use data contracts everywhere for the state of the service - as opposed to domain model objects we had in sprint 1.

Note that this is a temporary solution, we will migrate to a database at some point. That said, I suppose modifying data contracts is slightly easier than modifying the database -- I may be exaggerating the complexity of making changes to the databases since I haven't seen any database refactoring tools, and there must be some.

(When putting the reconstructed object graph' elements back to their collections we've iterated thru deserialized elements and added them to appropriate collections depending on the type of element).

Could post the code proving the concept works, if anyone is interested.

Generics

Generics this generics that. Surely, generics were one of the main hits of .Net FW 2.0 and you all know the advantages they give you, but what about disadvantages? The books I've read on software development are hardly giving anything for disadvantages, and that's suspicios because nothing is ideal and if you gain something, that means losing something the very same moment you gain.

The pain in the ass generics give you can be described as follows:
- generic classes and interfaces with more than two type parameters are hard to understand and maintain;
- generic class, say, List<B> is not convertible to List<A> if B is subclass of A (as of .Net FW 3.5), moreover there is no direct relationship between List<A> and List<B> which could be described in terms of OO paradigm;
- generics cypher the code to some extent: when you see an instance of Mine.MyGenericType<Mine.MyType1, Mine.MyType2, Mine.MyType2> in code you have to scratch your head to figure out which parameter means what, because they only have names internal to MyGenericType and don't mean anything outside of that class (this is somewhat less of a problem when you are writing the code, thanks to intellisense);
- generics used solely for type safety scare me a bit: the main drivers for introducing generics were code reuse, type safety and performance (in that order). There is usually a way or two to avoid using generics without losing type safety.

That's my humble opinion and don't get me wrong, I absolutely love generics. Just make sure you don't rely on them too much.

Buggy trace listener

Recently a colleague of mine ran into the troublesome TextWriterTraceListener. As the name suggests, it's a trace listener that writes trace messages to a file. The way you use it, as any other listener, is as follows: either you instantiate the listener in code and add it to the static Trace.Listeners collection, or let the runtime do the same thing for you by saying so in App.config -- then you dispatch trace messages to this and other trace listeners hooked up, thru the static Trace class.

The TextWriterTraceListener and the Trace class work together just fine, as long as you don't try to use them from a finalizer when your application is terminating. You say "Trace.Writeline("Hi John, got some bad news for you!")" in the finalizer of your class which happens to run -- among other cases -- during application shutdown, and doh! -- you get a marvelous error saying that the FILE has already been closed. Isn't it just nice?

(The listener references a FileStream which has a finalizer of its own and finalizers run in no particular order: chances are your finalizer (calling into Trace) will be out of luck, calling into a dead trace listener. There are several ways in which you can make that listener do a better job, but I ended up not using Trace and TextWriterTraceListener at all. This is definitely a design flaw in both Trace and that particular listener. It should be fixed from the inside, I don't want to work around this).