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Stop writing CLI validation. Parse it right the first time

(hackers.pub)
203 points dahlia | 1 comments | 06 Sep 25 18:20 UTC | HN request time: 0.298s | source
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12_throw_away ◴[07 Sep 25 01:29 UTC] No.45154518[source]▶
I like this advice, and yeah, I always try to make illegal states unrepresentable, possibly even to a fault.

The problem I run into here is - how do you create good error messages when you do this? If the user has passed you input with multiple problems, how do you build a list of everything that's wrong with it if the parser crashes out halfway through?

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1. geysersam ◴[07 Sep 25 06:43 UTC] No.45155934[source]▶
Maybe you can use his `or` construct to allow a `--server` without `--port`, but then also add a default `error_message` property.

After parsing you check if `error_message` exists and raise that error.