Objects

Objects are anonymous maps, which support defining and using arbitrary string keys.

let values = #{};
values["first"] = "bar";
values["second"] = 42;

dbg!(values["first"]);
dbg!(values.second); // items be accessed like struct fields.

if let Some(key) = values.get("not a key") {
    dbg!(key);
} else {
    println!("key did not exist");
}

for entry in values {
    dbg!(entry);
}

$> cargo run -- run scripts/book/objects/objects.rn
"bar"
42
key did not exist
("second", 42)
("first", "bar")

These are useful because they allow their data to be specified dynamically, which is exactly the same use case as storing unknown JSON.

One of the biggest motivations for Rune to have anonymous objects is so that we can natively handle data with unknown structure.

async fn get_commits(repo, limit) {
    let limit = limit.unwrap_or(10);

    let client = http::Client::new();
    let request = client.get(`https://api.github.com/repos/${repo}/commits`);
    let response = request.header("User-Agent", "Rune").send().await?;
    let text = response.text().await?;
    let json = json::from_string(text)?;

    let commits = json.iter().take(limit).map(|e| e.sha).collect::<Vec>();
    Ok(commits)
}

for commit in get_commits("rune-rs/rune", Some(5)).await? {
    println!("{commit}");
}

$> cargo run -- run scripts/book/objects/json.rn
9c4bdaf194410d8b2f5d7f9f52eb3e64709d3414
06419f2580e7a18838f483321055fc06c0d75c4c
cba225dad143779a0a9543cfb05cde9710083af5
15133745237c014ff8bae53d8ff8f3c137c732c7
39ac97ab4ebe26118e807eb91c7656ab95b1fcac
3f6310eeeaca22d0373cc11d8b34d346bd12a364

Using objects from Rust

Objects are represented externally as the Object type alias. The keys are always strings, but its value must be specified as the sole type parameter. Note that the dynamic Value can be used if the type is unknown.

use rune::alloc;
use rune::runtime::Object;
use rune::termcolor::{ColorChoice, StandardStream};
use rune::{Diagnostics, Vm};

use std::sync::Arc;

fn main() -> rune::support::Result<()> {
    let context = rune_modules::default_context()?;
    let runtime = Arc::new(context.runtime()?);

    let mut sources = rune::sources! {
        entry => {
            pub fn calc(input) {
                dbg(input["key"]);
                input["key"] = "World";
                input
            }
        }
    };

    let mut diagnostics = Diagnostics::new();

    let result = rune::prepare(&mut sources)
        .with_context(&context)
        .with_diagnostics(&mut diagnostics)
        .build();

    if !diagnostics.is_empty() {
        let mut writer = StandardStream::stderr(ColorChoice::Always);
        diagnostics.emit(&mut writer, &sources)?;
    }

    let unit = result?;

    let mut vm = Vm::new(runtime, Arc::new(unit));

    let mut object = Object::new();
    object.insert(alloc::String::try_from("key")?, rune::to_value(42i64)?)?;

    let output = vm.call(["calc"], (object,))?;
    let output: Object = rune::from_value(output)?;

    println!("{:?}", output.get("key"));
    Ok(())
}

$> cargo run --example object
42
Some("World")