How to implement TryFromChunks for external types?

[selfhoster1312]

I'm trying to parse a Multipart form into a struct that contains fields that are not defined in my crate, so i can't implement TryFromChunks for them. However they do implement FromStr, but implementing TryFromChunks for any types that implements FromStr would create implementation conflicts for most types...

These types also implement Deserialize. Maybe using serde::Deserialize instead of TryFromChunks could be an option (eg. behind a feature flag)?

[nerodono]

Currently serde doesn't support asynchronous parsing (e.g. you can't make the from_reader function async), so all purpose of the TryFromMultipart/TryFromChunks and so on is to make parsing asynchronous. Possibly there's another issue with that, so cc @murar8

[murar8]

Implementing the trait for external types directly is not possible AFAIK, we would need specialization to land on stable and it will be a long while if it ever does: https://github.com/rust-lang/rust/issues/31844

In the meanwhile your options are:

• Create a wrapper type and implement the trait on that.
• Open an issue and a contributor (usually myself) will implement the trait for the type. I am open to implement the trait for any stdlib types and for common rust crates.

[murar8]

Currently serde doesn't support asynchronous parsing (e.g. you can't make the from_reader function async), so all purpose of the TryFromMultipart/TryFromChunks and so on is to make parsing asynchronous. Possibly there's another issue with that, so cc @murar8

Yeah I don't even know if it would be possible to hack in a blanket implementation for any item that is deserializable so that's definitely a no-go in my opinion.

[pascalporedda]

Which types / external crates would you consider implementing the trait for?

I'd love if uuid and chrono would be supported

[murar8]

Sure I will look into it :+1:

[murar8]

Tracked in #46