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I am often in a situation where I have to design and code a process/algorithm, and there are different variants on that algorithm. For example, I am currently writing some database sychronisation code that has methods for download and upload. Those methods are similar, but not identical.
Having written the code, and got it to work, I am now refactoring it to remove the repetition.
I am not so bad at writing classes which mainly hold data, in those cases I find it easier at the beginning to apply entity-relationship modelling, break the data down into classes, and I can fairly quickly see common elements that can be put into base/abstract classes.
But I find it harder with algorithms/processes.
My questions are: is it better to take more time to design it up-front, thus avoiding the need for refactoring? And, if so, how do you get good at doing this?
I find that when I design up-front, because there is no way to test the design, I often go way off tangent and as soon as I start writing the code the design gets discarded. In contrast, with incremental development, you can regularly test your code to ensure it works. But the disadvantage of the way I do incremental development, is the extra time spent refactoring at the end so that I write "DRY" code.