Struct serde_with::MapPreventDuplicates

pub struct MapPreventDuplicates<K, V>(_);

Ensure no duplicate keys exist in a map.

By default serde has a last-value-wins implementation, if duplicate keys for a map 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 keys exist in a map.

The implementation supports both the HashMap and the BTreeMap from the standard library.

Example

#[serde_as]
#[derive(Deserialize)]
struct Doc {
    #[serde_as(as = "MapPreventDuplicates<_, _>")]
    map: HashMap<usize, usize>,
}

// Maps are serialized normally,
let s = r#"{"map": {"1": 1, "2": 2, "3": 3}}"#;
let mut v = Doc {
    map: HashMap::new(),
};
v.map.insert(1, 1);
v.map.insert(2, 2);
v.map.insert(3, 3);
assert_eq!(v, serde_json::from_str(s).unwrap());

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

Trait Implementations

impl<'de, K, V, KAs, VAs> DeserializeAs<'de, BTreeMap<K, V, Global>> for MapPreventDuplicates<KAs, VAs>where KAs: DeserializeAs<'de, K>, VAs: DeserializeAs<'de, V>, K: Ord,

fn deserialize_as<D>(deserializer: D) -> Result<BTreeMap<K, V>, D::Error>where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<'de, K, V, KAs, VAs, S> DeserializeAs<'de, HashMap<K, V, S>> for MapPreventDuplicates<KAs, VAs>where KAs: DeserializeAs<'de, K>, VAs: DeserializeAs<'de, V>, K: Eq + Hash, S: BuildHasher + Default,

fn deserialize_as<D>(deserializer: D) -> Result<HashMap<K, V, S>, D::Error>where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<'de, K, V, KAs, VAs, S> DeserializeAs<'de, IndexMap<K, V, S>> for MapPreventDuplicates<KAs, VAs>where KAs: DeserializeAs<'de, K>, VAs: DeserializeAs<'de, V>, K: Eq + Hash, S: BuildHasher + Default,

fn deserialize_as<D>(deserializer: D) -> Result<IndexMap<K, V, S>, D::Error>where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<K, KAs, V, VAs> SerializeAs<BTreeMap<K, V, Global>> for MapPreventDuplicates<KAs, VAs>where KAs: SerializeAs<K>, VAs: SerializeAs<V>,

fn serialize_as<S>( value: &BTreeMap<K, V>, serializer: S ) -> Result<S::Ok, S::Error>where S: Serializer,

Serialize this value into the given Serde serializer.

impl<K, KAs, V, VAs, H> SerializeAs<HashMap<K, V, H>> for MapPreventDuplicates<KAs, VAs>where KAs: SerializeAs<K>, VAs: SerializeAs<V>, H: ?Sized + Sized,

fn serialize_as<S>( value: &HashMap<K, V, H>, serializer: S ) -> Result<S::Ok, S::Error>where S: Serializer,

Serialize this value into the given Serde serializer.

impl<K, KAs, V, VAs, H> SerializeAs<IndexMap<K, V, H>> for MapPreventDuplicates<KAs, VAs>where KAs: SerializeAs<K>, VAs: SerializeAs<V>, H: ?Sized + Sized,

fn serialize_as<S>( value: &IndexMap<K, V, H>, serializer: S ) -> Result<S::Ok, S::Error>where S: Serializer,

Serialize this value into the given Serde serializer.