rust 40 lines · 6 steps

Parsing flexible JSON shapes with serde

How serde's untagged enums let one Rust type absorb multiple JSON representations of the same field.

Explained by highlit
Intermediate deserialization enums json type-modeling error-handling
1use serde::Deserialize;
2 
3#[derive(Debug, Deserialize)]
4#[serde(untagged)]
5enum StringOrNumber {
6 Number(f64),
7 Text(String),
8}
9 
10#[derive(Debug, Deserialize)]
11#[serde(untagged)]
12enum Id {
13 Numeric(u64),
14 Uuid(String),
15}
16 
17#[derive(Debug, Deserialize)]
18#[serde(untagged)]
19enum Recipient {
20 Single(String),
21 Many(Vec<String>),
22}
23 
24#[derive(Debug, Deserialize)]
25struct Notification {
26 id: Id,
27 to: Recipient,
28 #[serde(default)]
29 priority: StringOrNumber,
30}
31 
32impl Default for StringOrNumber {
33 fn default() -> Self {
34 StringOrNumber::Number(0.0)
35 }
36}
37 
38fn parse_notification(raw: &str) -> Result<Notification, serde_json::Error> {
39 serde_json::from_str(raw)
40}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Untagged enums let a single field accept several JSON shapes without custom parsing code.
  2. 2serde tries each enum variant in order and uses the first that deserializes successfully.
  3. 3Providing a Default lets serde fill in absent fields cleanly with #[serde(default)].

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