# Serde ignored
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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 = "0.0.3"
```
```rust
#[macro_use]
extern crate serde_derive;
extern crate serde;
extern crate serde_json;
extern crate serde_ignored;
use std::collections::{BTreeSet as Set, BTreeMap as Map};
#[derive(Debug, PartialEq, Deserialize)]
struct Package {
name: String,
dependencies: Map<String, Dependency>,
}
#[derive(Debug, PartialEq, Deserialize)]
struct Dependency {
version: String,
}
fn main() {
let j = r#"{
"name": "demo",
"dependencies": {
"serde": {
"version": "0.9",
"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
This crate is licensed under either of
* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
http://www.apache.org/licenses/LICENSE-2.0)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or
http://opensource.org/licenses/MIT)
at your option.
### Contribution
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.