Is it acceptable to create multiple classes in one .swift file, or should I create a separate .swift file for each class?

Question

Is it considered poor technique to create multiple classes in one swift file, or is it best to create a separate swift file for each class?

Answer 1

I have different answer for this question based on painful debugging and searching in the internet for last few days. I'm c++ dev with more than 15 years experience. Coming from this language I'm familiar with few design techniques which needs protected access. Since Swift doesn't support it and as it turns out they won't support it in near future, I've start using private access and write few classes in the same file. That way I've workaround the missing protected modifier (private functions are visible in the same file, so they will be visible for all classes in the same file, and if these classes are derived classes the private is actually working as protected). Well everything is fine and I was happy before found out that my application crashed with EXC_BAD_ACCESS code=1 ... The exceptions was not because of my code, it was because it layout of the members were somehow wrong. For example if i called one function a() from the derived class through instance variable the func b() was called. The b() was also member of the same class and was define before the a(). That is why some functions thrown bad access exception. Instance pointer was corrupt. After I moved all 3 classes to independent files everything looked fine.

Not sure that this was the actual reason or I've done something wrong, but not 100% of cases when you define multiple classes in the same file will be with defined behaviour. May be that is compiler problem, Swift is young language and even that I'm testing with Gold Master studio which is supposed to be stable, there are still a lot of bugs.