Consider using rustc_serialize::json::encode to obtain json

[hugoduncan]

Rather than force every structure to implement the ToJson trait, it might be preferable to allow users to just add a #[derive(RustcEncodable)] on their structs, and handlebars can obtain a JSON value via the rustc_serialize::json::encode function.

[vayn]

+1

And according to this post: What's the difference between the “serialize” and “rustc-serialize” crates?, I recommend to use Serde and its macros to serialize/deserialize a struct to/from JSON instead of rustc-serialize.

[hugoduncan]

I can second the recommendation for Serde, although it does require rust nightly to use it.

[sunng87]

Note that we don't actually serialize data to JSON. We just use the ToJson trait as a type system. Because handlebars is designed against JavaScript, whose type system isn't fully compatible with Rust. Currently, ToJson is a good way to convert Rust types into JavaScript types.

Yes, we need a macro for users to generate their ToJson impl easily.

[vayn]

Thanks. I understand why you use Json enum and ToJson trait for transforming Rust type and JavaScript type now. It is little twisted for the purpose though... Macro is a better and clearer way.

[sunng87]

@vayn patches are always welcomed :-)

[hugoduncan]

Another possibility, when using serde at least, would be to write your own Serializer implementation that returned a BTreeMap of values. This would remove the need to implement ToJson and the need for a custom macro.

[sunng87]

@hugoduncan I didn't look into Serde, is it easier to implement Serializer of Serde than ToJson of rustc-serialize?

Because most ToJson implementation will be: create a map, put every field into it. Perhaps we can find some meta-programming techniques to deal with this. Not sure if Rust has something for that.

[hugoduncan]

@sunng87 The Serializer would be something that rust-handlebars would implement. Users would then just mark structs with #[derive(Serialize)].

[sunng87]

@hugoduncan Iooked at Serde, I would like to implement a custom derive for handlebars that generates ToJson implementation. It would be compatible with current type system, but also reduce repeated ToJson impl.

[sunng87]

@hugoduncan @vayn check out tojson_macros I just made for generating default ToJson imp.

[vayn]

I'm still learning how to make a procedural macro for custom struct.

@sunng87 You're amazing! 👍

[sunng87]

@vayn :)

I'll close this for now. Feel free to reopen if there's any question.