Put me firmly in the camp of "optional fields are bad." I believe all fields should be required.
I come from an ONC/RPC background, which is the original UNIX RPC. Every iteration of an rpc would get versioned, and then you could write a conversion between versions, ex from V1 to V2, from V2 to V3, etc. This allowed for true backwards compatibility.
The idea of "forwards compatibility" is a pipedream, in my opinion. Just because something won't crash because a field is or isn't there doesn't mean that it will actually work. Code ages over time, and instead of looking at the spec, which will tell you which fields are required, you need to read the documentation, which may or may not tell you what is required. And especially when dealing with an older client, it simply may not work because what used to be optional-optional fields become required-optional fields.
It's the same argument as schemaless NOSQL database like Mongo vs MySQL. Having a schema is a pain in the ass, but it's better over time and ages much more gracefully than schemaless ones, because things won't just break.
I come from an ONC/RPC background, which is the original UNIX RPC. Every iteration of an rpc would get versioned, and then you could write a conversion between versions, ex from V1 to V2, from V2 to V3, etc. This allowed for true backwards compatibility.
The idea of "forwards compatibility" is a pipedream, in my opinion. Just because something won't crash because a field is or isn't there doesn't mean that it will actually work. Code ages over time, and instead of looking at the spec, which will tell you which fields are required, you need to read the documentation, which may or may not tell you what is required. And especially when dealing with an older client, it simply may not work because what used to be optional-optional fields become required-optional fields.
It's the same argument as schemaless NOSQL database like Mongo vs MySQL. Having a schema is a pain in the ass, but it's better over time and ages much more gracefully than schemaless ones, because things won't just break.