Hacker News Reader

Comment by Timwi | Hacker News Reader

You came so close. You realized that stopping at the first error is bad and you should continue. But then you still discard the entire deserialization when there's even a single error. You only needed one more step to realize that it might as well return the partial result alongside the errors.

The most common error in deserialization is when a field is missing. The most common reason for it missing is because it was added; an older version of the API didn't have it. Having the deserializer just bail out means the API cannot introduce a new field with a sensible default value and instead has to create a whole separate API endpoint that does the same thing.

View on HN

Can you explain how this would work if there weren't optional fields in your struct? Because if you're just suggesting that you use optional fields, that already works with vanilla serde.

Also, defaults for fields are already a vanilla serde feature.

No, you don't understand, but YOU are close ;) don't give up!

The whole point is to Make Illegal States Unrepresentable™. You see, if you WANT to allow a partial result, then you just encode it into the type with Option<T>, Result<T,E> or your own types. But if you DON'T want them, then you can sleep tight, assured that there won't be some nulls/nils/undefineds/zero-values creeping into the deepest core of your logic. Illegal values will be stopped at the border and denied entry. Values that are allowed to be "missing" (or similar, you can express a lot more here) can come in, but we know that they can be missing and must be handled on access (instead of NPEs, crashes, or worse: "default zero values").

In the spirit of http://www.catb.org/jargon/html/Z/Zawinskis-Law.html ...

"Every program attempts to expand until its clients and counterparties are so varied in protocol version (and implementation competency) that it must deserialize every field as optional, and handle said absence in business logic. Those programs which cannot so expand are replaced by ones which can."

(On a related note... I would give the world for Python to have optional chaining/safe navigation operators. The fact that Typescript is the Language that Makes Untrusted APIs Tolerable, while Python is the Language of Low-Level AI Iteration, and both have horrible ergonomics when trying to implement the other, is a source of endless frustration to me.)

But you can set defaults for fields when they are missing with serde.

Reply on news.ycombinator.com