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Are you joking “It compiles, ship it!”? You might actually be doing just that…

A while back, I talked with someone about using the Singleton Design Pattern vs. using an IoC container and registering your class as singleton.

Response:

IoC containers are regularly bootstrapped wrongly, resulting in your product not working as it should. And you don’t discover that until you startup the product. I’d rather use the Singleton Pattern. That way, the compiler will protect against errors.

A composite validator pattern

Have you ever encountered something like this?
(Note: #r denotes a collapsed region of code)

public class MyBulkyClassThatDoesALot
{
    #r Private fields
    #r Constructor
    #r Another constructor
    #r Public properties
    #r Public methods
    #r Private methods

    #region Validation

    // meanwhile, somewhere on line 20485
    public ValidationResult Validate()
    {
        ValidationResult result;
        CheckThatSomethingHolds(result);
        CheckThatSomethingElseHolds(result);

        if (this.somesituation)
        {
            CheckSituationDependentCondition(result);
            CheckSituationDependentOtherCondition(result);
        }

        ...
        // Somewhere on line 20585
        CheckLastThing(result);
        return result;
    }

    private void CheckThatSomethingHolds(ValidationResult result)
    {
        if (this.somecondition)
        {
            result.AddError(new ValidationError("Condition X failed"));
        }
    }

    private void CheckThatSomethingElseHolds(ValidationResult result)
    {
        if (this.somecondition)
        {
            result.AddError(new ValidationError("Condition Y failed"));
        }
    }

    private void CheckSituationDependentCondition(result)
    {
        if (this.somecondition)
        {
            result.AddError(new ValidationError("Condition SituationDependent1 failed"));
        }
    }

    // Are you tired of scrolling yet? Good, because this is how whomever reads this code shall feel in real life ;)

    private void CheckSituationDependentOtherCondition(result) { ... snip }

    // A sigh of relief when you reach the last one
    private void CheckLastThing(ValidationResult result)
    {
        if (this.somecondition)
        {
            result.AddError(new ValidationError("Condition Z failed"));
        }
    }

    #endregion Validation

    // And then, of course, there is a lot of code after this. If you're unlucky, there wasn't even a #region around all the Validation methods and you have to hunt them down one by one because they are scattered through the code.
}

Don’t worry, you’re not the first one to end up with this. Often, it started as a single validation rule that was just implemented directly in the class to be validated. However, there are some things to look out for.