I’ve refactored a large js code base into ts. Found one such bug for every ~2kloc. The obvious ones are found quickly in untyped code, the problem is in rare cases where you e.g. check truthiness on something that ends up always true.
Of those bugs I wondered how much a type would help. For example is it a misunderstanding of business requirements (nosurcharge bool = iscash
bool) or a “typo” / copy paste error. If the former types don’t help. The latter they might.
It definitely helps in larger applications where things are named similarly, especially if you're dealing with a massive DB schema. If you have some method to update some data where all the PRs are longs and it has the signature "update(long,long)", passing the wrong long value would be disastrous. Even if this type of error is 1:10k LOC, using wrapper classes pretty much eliminates this bug.
In our codebase, we use wrapper classes and the only time we had a defect with this is when one developer got lazy and used 3 primitive Strings in a class instead of wrapper classes. Another developer needed to update the code and populated the wrong wrapper class as they were not as familiar with that part of the codebase. Had the original developer simply used wrapper classes, the person maintaining the code wouldn't have had that confusion.
