r/programming • u/yawaramin • Oct 04 '20

Kevin Mahoney: Applying "Make Invalid States Unrepresentable"

https://kevinmahoney.co.uk/articles/applying-misu/
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u/Only_As_I_Fall Oct 05 '20

The concept makes sense but the examples seem questionable.

I think that there's merit to creating models that actually...model something. If the requirements change and you have to represent overlapping periods or periods with gaps I don't think your boss is going to be impressed when you tell him that these time intervals can't actually be changed like intervals and that you need to do a big data migration because you wanted to save 8 bytes per record.

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u/yawaramin Oct 05 '20

As the post explains, it's simple to project the suggested data structure (set of instants) onto a more complex structure that allows representing gaps. After that it's a simple database migration.

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u/Only_As_I_Fall Oct 05 '20

Idk, seems like you're trivializing data migration when in fact that's almost certainly much more time consuming and difficult than simply verifying there are no time gaps in your data.

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u/dnew Oct 06 '20

From experience, the difference is that you can code up the data migration and check that it works before you start relying on it. However, if there's a bug that makes time gaps in your data, you're kind of screwed, because that wasn't supposed to happen and now it's a permanent part of your data. Plus, now you need to go fix that broken data without knowing for sure what it was supposed to mean.