Comment by makecheck
6 years ago
The “exists” state is dynamic (something else in the system could be in the process of deleting the file since it was last checked). It’s more reliable if you don’t check in advance and simply try to open the file every time you need it. You handle errors while opening the file.
This is really interesting. For systems programming, files usually have clear ownership and modification context. If I call exists(), it should still exists for as long as that thread is paused.
It's an anti-pattern to throw errors for expected behavior.
Which is why you don't throw errors but return a result type such as Rust's Result, Haskell's Either, or C++'s upcoming std::expected :)
On the other hand, non-atomically asking for permission first in any concurrent (or re-entrant!) context is not just an antipattern but simply wrong and always a possible race condition. It is impossible to write a routine that tries to open a file and is statically guaranteed to succeed.
The idea appears to me to have been popularized by python, where it's straight called an antipattern to do the check beforehand [0]. The language also uses exceptions for standard control flow - for example, there's one called StopIteration that the language uses to indicate to loops that the current generator or iterator has reached its end.
[0] https://docs.quantifiedcode.com/python-anti-patterns/readabi...