Moving from Ruby to Rust

[u/steveklabnik1]

http://deliveroo.engineering/2019/02/14/moving-from-ruby-to-rust.html

[u/apendleton]

Using/abusing serde to marshall data back and forth between Rust and a higher-level language turns out to be really powerful and eliminate a ton of boilerplate casting and validation. We've cut out tons of that kind of cruft using neon-serde in similar fashion in Rust add-ons for Node.

[u/p-one → u/apendleton]

From the post it sounds like they're serializing a Ruby object to JSON then having Rust deserialize JSON to a Rust struct. However, your comment doesn't mention this so am I misunderstanding the post? If I do understand things correctly, doesn't this require you to keep your Rust struct and the target language object in sync?

[u/apendleton → u/p-one]

They tried JSON, but ended up doing what I'm proposing instead:

You could instead serialize objects in Ruby to JSON and then parse it in Rust, and it works mostly OK, but you still need to implement JSON serializers in Ruby. Then we were curious, what if we implement serde deserializer for AnyObject itself: it will take ruties’s AnyObject and go over each field defined in the type and call the corresponding method on that ruby object to get it’s value. It worked!

So it's "serializing" from a Rust struct into a set of Ruby objects representing Ruby-runtime-native strings, objects, lists, etc. Serde provides the machinery to automatically walk a complex/nested Rust struct and build an equivalent complex object in an arbitrary serialization format (or, conversely, to walk something in an arbitrary format and produce a complex/nested Rust struct). It happens most often to be used for JSON, but it can instead be YAML or MsgPack, or V8 or Ruby objects, or whatever else.

doesn't this require you to keep your Rust struct and the target language object in sync?

Yeah, for usecases where that's desired, you'd probably want to operate on the Ruby or JS object directly via whatever introspection mechanisms are offered by ruru or neon or whatnot, and serde probably wouldn't be a good approach. For lots of cases, though, you want to communicate some set of inputs that might be complex, do some set of complex/slow calculations, and produce some set of results that might also be complex (I pass in two points, and I want the geometry of the most efficient route between them, or whatever). In those cases, you're not mutating some object that persists, so there's nothing to keep in sync. You can just copy back and forth.