[Groxx]

>the failures were silent, so you'd end up with missing data everywhere without knowing it for weeks.

This is the main reason I think protobuf's "zero values are simply not communicated" is fundamentally wrong. Missing data is one of the easiest flaws to miss, and it tends to cause problems far away from the source of the flaw, in both time and space, which makes it extremely hard to notice and fix.

I get the arguments in its favor. I get the arguments in favor of "everything is optional by default". But presence is utterly critical in detecting flaws like this, and it can't always be addressed in a backwards-compatible way by application code. E.g. in proto's case, it's not possible because that data does not exist, and adding it would change the binary data. Even binary-compatible workarounds like "add a field with a presence fieldset" aren't usable because that unrecognized field will be silently ignored by older consumers, so you're right back to where you started.

It needs to exist from day 1 or you're shooting your users in the feet.