Struct KeyValueMap

pub struct KeyValueMap<T>(/* private fields */);

Convert Vec elements into key-value map entries

This maps a single struct/tuple/etc. to a map entry. The map key is converted to a struct field. The other values will be mapped to the map value.

The conversion supports structs, tuple structs, tuples, maps, and sequences. Structs need a field that is named $key$ to be used as the map key. This can be done with the #[serde(rename = "$key$")] attribute. Maps similarly need a map-key that is named $key$. For tuples, tuple structs, and sequences the first element is used as the map key.

Examples

Struct with String key in JSON

use serde_with::{serde_as, KeyValueMap};

#[derive(Serialize, Deserialize)]
struct SimpleStruct {
    b: bool,
    // The field named `$key$` will become the map key
    #[serde(rename = "$key$")]
    id: String,
    i: i32,
}

#[serde_as]
#[derive(Serialize, Deserialize)]
struct KVMap(
    #[serde_as(as = "KeyValueMap<_>")]
    Vec<SimpleStruct>,
);

// ---

// This will serialize this list of values
let values = KVMap(vec![
    SimpleStruct {
        b: false,
        id: "id-0000".to_string(),
        i: 123,
    },
    SimpleStruct {
        b: true,
        id: "id-0001".to_string(),
        i: 555,
    },
    SimpleStruct {
        b: false,
        id: "id-0002".to_string(),
        i: 987,
    },
]);

// into this JSON map
let expected =
r#"{
  "id-0000": {
    "b": false,
    "i": 123
  },
  "id-0001": {
    "b": true,
    "i": 555
  },
  "id-0002": {
    "b": false,
    "i": 987
  }
}"#;

// Both serialization and deserialization work flawlessly.
let serialized = serde_json::to_string_pretty(&values).unwrap();
assert_eq!(expected, serialized);
let deserialized: KVMap = serde_json::from_str(&serialized).unwrap();
assert_eq!(values, deserialized);

Tuple struct with complex key in YAML

use serde_with::{serde_as, KeyValueMap};
use std::net::IpAddr;

#[derive(Serialize, Deserialize)]
struct TupleStruct (
    // The first element in a tuple struct, tuple, or sequence becomes the map key
    (IpAddr, u8),
    bool,
);

#[serde_as]
#[derive(Serialize, Deserialize)]
struct KVMap(
    #[serde_as(as = "KeyValueMap<_>")]
    Vec<TupleStruct>,
);

// ---

// This will serialize this list of values
let values = KVMap(vec![
    TupleStruct(
        (IpAddr::from_str("127.0.0.1").unwrap(), 8),
        true
    ),
    TupleStruct(
        (IpAddr::from_str("::1").unwrap(), 128),
        true
    ),
    TupleStruct(
        (IpAddr::from_str("198.51.100.0").unwrap(), 24),
        true
    ),
]);

// into this YAML
let expected =
r#"? - 127.0.0.1
  - 8
: - true
? - ::1
  - 128
: - true
? - 198.51.100.0
  - 24
: - true
"#;

// Both serialization and deserialization work flawlessly.
let serialized = serde_yaml::to_string(&values).unwrap();
assert_eq!(expected, serialized);
let deserialized: KVMap = serde_yaml::from_str(&serialized).unwrap();
assert_eq!(values, deserialized);

Trait Implementations

impl<'de, T, TAs> DeserializeAs<'de, Vec<T>> for KeyValueMap<TAs>

where TAs: DeserializeAs<'de, T>,

fn deserialize_as<D>( deserializer: D, ) -> Result<Vec<T>, <D as Deserializer<'de>>::Error>

where D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl<T, TAs> SerializeAs<Vec<T>> for KeyValueMap<TAs>

where TAs: SerializeAs<T>,

fn serialize_as<S>( source: &Vec<T>, serializer: S, ) -> Result<<S as Serializer>::Ok, <S as Serializer>::Error>

where S: Serializer,

Serialize this value into the given Serde serializer.