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> It would be MUCH harder to debug a complex parsing function than a regex with Regex101. I encountered, this week, a 42-line function that determines if a num

> It would be MUCH harder to debug a complex parsing function than a regex with Regex101. I encountered, this week, a 42-line function that determines if a number is a valid string representation of a double. The function is wrong and has been wrong for a decade or more. The code is obtuse using unclear state variables (multiple boolean flags) to accept or reject the string at various points. It could have been a regex, and we could have seen at (almost) a glance what was intended. There are several other functions in the same file doing similar things so this ended up being something like 300+ lines of both wrong and difficult to understand code that could have been maybe 30 total lines of relatively easy to read and debug regexes.

throwanem 4y ago
Yeah, I'd definitely replace that whole function - with a try/catch-wrapped (or NaN-checked, etc.) attempt to parse the string as a double. Not a regex, which then still would have to be tested to make sure it's exactly as strict as whatever parser it's going to be passed to, anyway.
- Jtsummers 4y ago
  Fair, but I'm not even sure where this value ends up yet so I don't want to parse it (vice validate it), just getting it to reject "1-2" as a double would be a start (currently accepted, note that it's not accepting expressions just values). Stage one of fixing this thing is just tackling obviously wrong code like this, their creative shared pointer implementation that's also wrong (the memory will be freed while other pointers still have access to it, and the reference counter is not in the shared pointer but the object it contains so checking the reference counter at that point will result in use-after-free errors), and their fantastic use of iterators that will crash the program if that code is ever called (they didn't understand iterator invalidation). And yesterday I found that they read a file (in its entirety!) one character at a time, tacking the results onto the end of a string. There is no parsing logic at that point, it's literally just building a giant string. And all of that is in what should be straightforward logic any trained novice can handle, the real critical code which solved a somewhat novel problem (not novel novel, but not an everyday problem) gets even more creative.
  - throwanem 4y ago
    By the sound of it, this may well indeed be the rare case in which jwz's dictum fails to hold, and using a regex will yield one problem fewer - or, failing that, maybe kick a hole in the side and go looking for a river or two. In any case, good luck...

throwanem 4y ago

Yeah, I'd definitely replace that whole function - with a try/catch-wrapped (or NaN-checked, etc.) attempt to parse the string as a double. Not a regex, which then still would have to be tested to make sure it's exactly as strict as whatever parser it's going to be passed to, anyway.

Jtsummers 4y ago
Fair, but I'm not even sure where this value ends up yet so I don't want to parse it (vice validate it), just getting it to reject "1-2" as a double would be a start (currently accepted, note that it's not accepting expressions just values). Stage one of fixing this thing is just tackling obviously wrong code like this, their creative shared pointer implementation that's also wrong (the memory will be freed while other pointers still have access to it, and the reference counter is not in the shared pointer but the object it contains so checking the reference counter at that point will result in use-after-free errors), and their fantastic use of iterators that will crash the program if that code is ever called (they didn't understand iterator invalidation). And yesterday I found that they read a file (in its entirety!) one character at a time, tacking the results onto the end of a string. There is no parsing logic at that point, it's literally just building a giant string. And all of that is in what should be straightforward logic any trained novice can handle, the real critical code which solved a somewhat novel problem (not novel novel, but not an everyday problem) gets even more creative.
- throwanem 4y ago
  By the sound of it, this may well indeed be the rare case in which jwz's dictum fails to hold, and using a regex will yield one problem fewer - or, failing that, maybe kick a hole in the side and go looking for a river or two. In any case, good luck...