How to decode JSON object with Rust keyword attribute name?

Question

I was wondering if it is possible to decode a JSON object in Rust that has an attribute name which is also a Rust keyword. I am working with the rustc-serialize crate and my struct definition looks like this:

#[derive(RustcDecodable)]
struct MyObj {
  type: String
}

The compiler throws an error because type is a keyword:

error: expected identifier, found keyword `type`
src/mysrc.rs:23     type: String,
                           ^~~~

Is it safe to assume that the original data can't be changed to avoid the conflict? — Shepmaster
– Shepmaster, Commented Mar 17, 2015 at 17:42
yes, it would be best if i didn't have to change the source data. I guess maybe creating a new struct field with a different name and writing a custom impl Decodable is the only way? — rking788
– rking788, Commented Mar 17, 2015 at 18:34
I can see either manually implementing it or using Json::from_str and then poking into its result value. — Shepmaster
– Shepmaster, Commented Mar 17, 2015 at 18:57

oli_obk · Accepted Answer · 2017-01-31 07:29:02Z

27

You can use the serde crate. It supports renaming of fields since February 2015

Your example could then look like this:

#[derive(Deserialize)]
struct MyObj {
    #[serde(rename = "type")] 
    type_name: String
}

edited Jan 31, 2017 at 7:29

answered Mar 18, 2015 at 9:28

oli_obk

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2 Comments

rking788 Over a year ago

Seems like exactly what i was looking for. It says it does some lookahead, do you know if it is possible to parse an attribute that could be one of a few different types? so a field called msg could be either a JSON string or an array.

oli_obk Over a year ago

That is one of the main reasons serde was invented, because the old deserializer couldn't read an enum without having read a tag beforehand.

Anders Evensen · Accepted Answer · 2022-10-29 16:03:46Z

2

This can be done without serde's field renaming by using raw identifiers. By adding r# in front of an identifier, a keyword name can be used.

Using `rustc-serialize`

#[derive(RustcDecodable)]
struct MyObj {
    r#type: String
}

Using `serde`

use serde::Deserialize;

#[derive(Deserialize)]
struct MyObj {
    r#type: String
}

Note that rustc-serialize is deprecated in favor of serde.

answered Oct 29, 2022 at 16:03

Anders Evensen

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