I agree with you in general, but I think a better rule would be to almost never rewrite code.
I know that everyone thinks their predecessor was an idiot. And I agree that full rewrites are usually a bad idea. But sometimes, the predecessor genuinely was an idiot, and the code really is that bad. If the use cases and inputs and desired outputs are well documented enough, a full rewrite can be the right choice.
It depends on the size of the system, too. A full rewrite of something as complex as Netscape is asking for trouble. If it's something that can be rewritten in a day, or even a few weeks, it might okay to go ahead and do it.
Of course, by the time you've got enough experience to accurately estimate how long a rewrite will take, you've probably got enough experience to just refactor the old code without going insane.
If the inputs and outputs and the use cases are understood and it’s akready working, create an anti corruption layer and treat it like a 3rd party binary blob.
I know that everyone thinks their predecessor was an idiot. And I agree that full rewrites are usually a bad idea. But sometimes, the predecessor genuinely was an idiot, and the code really is that bad. If the use cases and inputs and desired outputs are well documented enough, a full rewrite can be the right choice.
It depends on the size of the system, too. A full rewrite of something as complex as Netscape is asking for trouble. If it's something that can be rewritten in a day, or even a few weeks, it might okay to go ahead and do it.
Of course, by the time you've got enough experience to accurately estimate how long a rewrite will take, you've probably got enough experience to just refactor the old code without going insane.