Module sets_duplicate_value_is_error

Ensure no duplicate values exist in a set.

By default serde has a last-value-wins implementation, if duplicate values for a set exist. Sometimes it is desirable to know when such an event happens, as the first value is overwritten and it can indicate an error in the serialized data.

This helper returns an error if two identical values exist in a set.

The implementation supports both the HashSet and the BTreeSet from the standard library.

Converting to serde_as

The same functionality can be more clearly expressed using the serde_as macro and SetPreventDuplicates. The _ is a placeholder which works for any type which implements Serialize/Deserialize.

#[serde_as]
#[derive(Deserialize, Serialize)]
struct A {
    #[serde_as(as = "SetPreventDuplicates<_, _>")]
    s: HashSet<usize>,
}

Example

#[derive(Deserialize)]
struct Doc {
    #[serde(with = "::serde_with::rust::sets_duplicate_value_is_error")]
    set: HashSet<usize>,
}

// Sets are serialized normally,
let s = r#"{"set": [1, 2, 3, 4]}"#;
let v = Doc {
    set: HashSet::from_iter(vec![1, 2, 3, 4]),
};
assert_eq!(v, serde_json::from_str(s).unwrap());

// but create an error if duplicate values, like the `1`, exist.
let s = r#"{"set": [1, 2, 3, 4, 1]}"#;
let res: Result<Doc, _> = serde_json::from_str(s);
assert!(res.is_err());

Functions

• deserialize
  Deserialize a set and return an error on duplicate values
• serialize
  Serialize the set with the default serializer