I'm not sure I would prefer the second version in a code review. I find the first version is conceptually nicer because it's easy to see that you will always get the correct count. In the second version you have to enforce that invariant yourself and future code changes could break it.
If this is premature optimization or not depends on the size of the array, number of loop iterations and how often that procedure is called. If that's an optimization you decide to do, I think it would be nice to extract this into an "ArrayWithLength" data structure that encapsulates the invariant.
> In the second version you have to enforce that invariant yourself and future code changes could break it.
Yes, that's a real issue. But we've been given two options:
- Does the correct thing, and will continue to do the correct thing regardless of future changes to the code. Will break if the use case changes, even if the code never does.
- Does the correct thing, but will probably break if changes are made to the code. Will work on any input.
It actually seems a lot more likely to me that the input given to the code might change than that the code itself might change. (That's particularly the case for the original post, where the code serves to read a configuration file, but it's true in general.)
Yes, I absolutely see the reasoning and I think if one does go the route of encapsulating the more efficient array logic one can have the best of both options.
> if one does go the route of encapsulating the more efficient array logic one can have the best of both options.
Do you see a way to do this that doesn't involve rolling your own array-like or list-like data type and replacing all uses of ordinary types with the new one? (This is actually already the implementation of standard Python types, but if you're encountering the problem, it isn't the implementation of your types.)
I guess it depends on the language and library you are using but I have the feeling that in most cases one would probably need to replace the usage of the old data type with the new one.
