Write a struct to a YAML file in Rust · oneyaml Rust cookbook

Derive serde’s Serialize and call oneyaml::to_string. Fields come out in declaration order, in block style.

Terminal

cargo new write-yaml && cd write-yaml
cargo add [email protected] serde -F serde/derive

Put this in src/main.rs and run cargo run:

RUST

use serde::{Deserialize, Serialize};
use std::collections::BTreeMap;
 
#[derive(Debug, Serialize, Deserialize, PartialEq)]
#[serde(rename_all = "camelCase")]
struct Service {
    name: String,
    image: String,
    replica_count: u32,
    ports: Vec<u16>,
    env: BTreeMap<String, String>,
    #[serde(skip_serializing_if = "Option::is_none")]
    healthcheck: Option<String>,
    note: String,
}
 
fn main() -> Result<(), Box<dyn std::error::Error>> {
    let svc = Service {
        name: "web".into(),
        image: "nginx:1.27".into(),
        replica_count: 2,
        ports: vec![80, 443],
        env: BTreeMap::from([("LOG_LEVEL".into(), "info".into())]),
        healthcheck: None,
        note: "no".into(),
    };
 
    let yaml = oneyaml::to_string(&svc)?;
    std::fs::write("service.yaml", &yaml)?;
    print!("{yaml}");
 
    // Read it back: the same value.
    let back: Service = oneyaml::from_str(&std::fs::read_to_string("service.yaml")?)?;
    println!("round trip equal: {}", back == svc);
    Ok(())
}

Text

name: web
image: nginx:1.27
replicaCount: 2
ports:
  - 80
  - 443
env:
  LOG_LEVEL: info
note: 'no'
round trip equal: true

healthcheck is None and skip_serializing_if leaves it out; without it, it’s written as null. to_writer writes to any io::Write, and to_string_with takes SerializeSettings.

Limits

No comments. A struct has nowhere to keep them, so the output has none. To change a file people maintain by hand and keep its comments, edit it as a Document: edit YAML and keep its comments.
Strings stay strings for every reader. A string that another reader could take for a different type is quoted: note is written 'no', so YAML 1.1 tools don’t read it as false (the Norway problem).

To read the file into the struct: parse YAML into a struct.