[hot_gril]

Not really one domain in particular, just internal services in general. In many cases, the field is intended to be required in the first place. If not, surprisingly 0 isn't a real answer a lot of the time, so it means none or default: any kind of numeric ID that starts at 1 (like ticket numbers), TTLs, error codes, enums (0 is always UNKNOWN). Similarly with empty strings.

I have a hard time thinking of places I really need both 0 and none. The only example that comes to mind is building room numbers, in some room search message where we wanted null to mean wildcard. In those cases, it's not hard to wrap it in a message. Probably the best argument for optionals is when you have a lot of boolean request options where null means default, but even then I prefer instead naming them such that the defaults are all false, since that's clearer anyway.

It did take some getting used to and caused some downstream changes to how we design APIs. I think we're better for it because the whole null vs 0 thing can be tedious and error-prone, but it's very opinionated.

[kortex]

Any time you have a scalar/measurement number, basically any value with physical units, counts, percentages, anything which could be in the denominator of a ratio, those are all strong indicators of a "semantic zero" and you really want to tell the difference between None and 0. They are usually floats, but could be ints (maybe you have number_of_widgets_online, 0 means 0 units, None means "idk".)

[hot_gril]

What's the difference between none inches and 0 inches? Might need a concrete example. We deal with space a fair amount and haven't needed many optionals there.

[TwentyPosts]

They just gave a concrete example: The difference between "we don't know" and "we know that it's zero".

Here's another fun one: I've seen APIs where "0.0" was treated as "no value, so take the default value". The default value happened to be 0.2.

[jakjak123]

I had the same experience. It was a bit awkward for 6 months, but down the line we learned to design better apis, and dealing with nullable values are tedious at best. Its just easier knowing that a string or integer will _never_ cause a nullpointer.

[sebastos]

Huh, yeah I see. I guess I work more on the robotics side where messages often contain physical or geometric quantities, and that colors my thinking a bit. So "distance to that thing = 0" is a very possible situation, and yet you also want to allow it to say "I didn't measure distance to that thing". And those are very distinct concepts you never want to conflate.

[hot_gril]

I can see that. Or the rare situations where I needed 0 vs null, if for some reason that situation was multiplied times 100, I'd start wanting an optional keyword.