# Serde ignored
[
](https://github.com/dtolnay/serde-ignored)
[
](https://crates.io/crates/serde_ignored)
[
](https://docs.rs/serde_ignored)
[
](https://github.com/dtolnay/serde-ignored/actions?query=branch%3Amaster)
Find out about keys that are ignored when deserializing data. This crate
provides a wrapper that works with any existing Serde `Deserializer` and invokes
a callback on every ignored field.
You can use this to warn users about extraneous keys in a config file, for
example.
Note that if you want unrecognized fields to be an error, consider using the
`#[serde(deny_unknown_fields)]` [attribute] instead.
[attribute]: https://serde.rs/attributes.html
```toml
[dependencies]
serde = "1.0"
serde_ignored = "0.1"
```
```rust
use serde::Deserialize;
use std::collections::{BTreeSet as Set, BTreeMap as Map};
#[derive(Debug, PartialEq, Deserialize)]
struct Package {
name: String,
dependencies: Map,
}
#[derive(Debug, PartialEq, Deserialize)]
struct Dependency {
version: String,
}
fn main() {
let j = r#"{
"name": "demo",
"dependencies": {
"serde": {
"version": "1.0",
"typo1": ""
}
},
"typo2": {
"inner": ""
},
"typo3": {}
}"#;
// Some Deserializer.
let jd = &mut serde_json::Deserializer::from_str(j);
// We will build a set of paths to the unused elements.
let mut unused = Set::new();
let p: Package = serde_ignored::deserialize(jd, |path| {
unused.insert(path.to_string());
}).unwrap();
// Deserialized as normal.
println!("{:?}", p);
// There were three ignored keys.
let mut expected = Set::new();
expected.insert("dependencies.serde.typo1".to_owned());
expected.insert("typo2".to_owned());
expected.insert("typo3".to_owned());
assert_eq!(unused, expected);
}
```
#### License
Licensed under either of Apache License, Version
2.0 or MIT license at your option.
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
be dual licensed as above, without any additional terms or conditions.