What conversion/rewrite have you been involved with that failed? What where the languages and framework involved in the process? How large was the software in question? Finally what is the top one or two thing you learned from being involved with the process.
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One of my favorites was a fixed price project developing a server app on Sun OS 3 that was eventually required to run on an old Data General machine running some (at the time) current version of Unix.
Now, we knew ahead of time it would be painful porting the C code to the Data General because it had 9 bit bytes / 36 bit words but didn't realize how ... lacking... the Unix implementation would be.
It was approximately 5 hours from the start of the porting task when the wise executive decision was made to simply buy the customer a shiny new Sun box.
I had one recently that largely failed due to my inability to thoroughly convince management that rewriting the app would be cheaper in the long run than to keep maintaining it as it was. If I had only read up on technical debt sooner, it may have been a success. Jeff's latest article on the topic was about 8 months too late for me!
All told the app was about 75K lines of C# code but it was a maintenance nightmare (in-house application). A handful of god classes and the rest were what I called puppet classes (classes by name only, the god classes "pulled the strings" for everything they did). Almost nothing was user-configurable so developers were responsible for everything.
In hindsight, the biggest roadblock to success was the app itself. Keeping it running was a full-time job for 3 of us. I think the best thing we could have done was to keep on refactoring. The "version 2" app had some real good concepts and we should have kept on trying to get them integrated instead of starting over... Had we done that, we could have built the big components after stabilizing the original app.
I once attempted to port a game I wrote in DarkBasic to C.
The problem I ran into was that DarkBasic was such a limited language (for example, no argument passing by reference) when I ported it I attempted to do a straight port... IE, I tried not to refactor it appropriately for the language I was using...
The result was a big mess...
I probably could have gotten it working, but I stopped after about 2 days because I realized it needed more than just translation to move to C...
I had written a Pacman clone using C and Allegro back in the day and I tried to rewrite it to run on the Dreamcast.
That was some horrible code. I couldn't really salvage much from the code base and scrapped the idea.
I learned that regardless of what I thought at the time, I was a really horrible programmer back then and I had learned a lot in the passing years. It also made me realize that in a few years time, I should learn enough to look back on the code I was writing today and think the same thing. Basically, I should always strive to become better.
I was once asked to convert a program which drove a photo typsetter on a DEC-System10 to IBM 4381. Looking at the code, I discovered that the original developer had, for no obvious reason, written various bits of the program in the following different languages:
This was a great testimony to DEC's support for multi-language programming, but it was the only time I've had to go to a user and say "No can do".