Debugging Challenge #2

Previously on Dr. Lambda's blog:

I have deviced a series of debugging challenges, some are easy, some are really hard, all come from real live systems. Good luck!

The Challenge

• 1 point if you can spot where the error is.
• +1 point if you can explain why.
• +2 points if you can explain how to fix it.

export class ActivityService {
    activities : Activity[] = [];
    constructor(){
        this.activities = [
            {
                title: "Arrange meeting",
                type: "task"
            }
        ];
        setTimeout(function () {
            this.activities.push({ 
                title: "Meeting",
                type: "appointment"
            });
        }, 3000); 
    };
}

Debugging Challenge #1

Previously on Dr. Lambda's blog:

I have deviced a series of debugging challenges, some are easy, some are really hard, all come from real live systems. Good luck!

The Challenge

• 1 point if you can spot where the error is.
• +1 point if you can explain why.
• +2 points if you can explain how to fix it.

private static long IncrementRowVersion(long rowversion)
{
    return rowversion++;
}

Bug Hunt: Debugging Challenge #0

So, I really like puzzles, and challenges. Just like the Javascript Drinking Game. I also used to post programming challenges online, most were extremely challenging, and very time consuming. Therefore I have long been thinking how to make exercises that are both challenging, relevant, and light.

My idea was some sort of debugging challenge. As a developer I spend most of my time doing this anyway, so I figured my colleagues must too, and it would be great practice. Because we are living in a culture were attention span is getting shorter and shorter I knew that the entire thing has to fit on a page, the description should be bulleted, and the code cannot be more than a handful of lines. If any of these fail most people wont give it a second glance.

I decided on a simple point system, starting with a pretty trivial task – to hook the reader. Just identify what looks wrong. Then draw them in by asking why they said that, and finally the real challenge: How to fix it. The Bug Hunt has a start date and an end date, and everybody collects points all season. At the end the victor can have his pick of which project to work on.

After spending a year keeping an eye out, I finally feel like I have collected enough material for the first "season". All the code comes from actual live systems that I have come in contact with as a consultant. They are obviously annonymized, but the structure of the code, and more importantly the bugs were real. As such, the challenges have very different flavor, some are included because they are very difficult, others are deceptively easy. They span different programming languages and technologies, however, in most cases this context must be inferred.

I highly recommend that you share challenges that you like (I print and hang them on the walls in the office), you might even use them to set up a Bug Hunt at your own office. If so, I would be happy to provide the answers.

Let the 0th Bug Hunt begin, and a good hunt to all participants!

The Challenge

• 1 point if you can spot where the error is.
• +1 point if you can explain why.
• +2 points if you can explain how to fix it.

SELECT a.* FROM Notification a
LEFT OUTER JOIN (
    SELECT CONVERT(uniqueidentifier, 
                MIN(CONVERT(char(36), b.[ID]))) AS ID
            , CAST(b.[Message] AS varchar(255)) AS Message_varchar
            , b.[To]
    FROM Notification b
    GROUP BY Message_varchar, b.[To]
) AS KeepRows ON
a.[ID] = KeepRows.[ID]
WHERE a.[Sent] = 0
AND KeepRows.[ID] IS NULL