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Comment by 3pt14159 | Hacker News Reader

If you want to treat a number like a string, why not just treat it like a string? When people enter zip codes online they enter 07045, so why not just store that? Even forget about other countries like Canada it seems like the best way...

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There are lots of way to accidentally lose a leading zero along the way. For a quick and realistic example make a csv file the looks like:

   01234,Hello

import it into Excel, edit something and export it as csv again. Unless you pay careful attention to what you're doing, you've just lost your leading zero.

Agreed - if you're going to validate anything at all, define a new type and don't hide the constraints checking within a secret unit testing lair. I hope I would be agnostic about the code here though, there is no point rewriting poorly conceived stringly typed code - that's a symptom that such efforts would be part of a losing battle

The code was for handling zipcodes from a CSV file so we don't really know where the data came from.

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